The 'Storage Almost Full' alert is back. Last time a cleaning app scanned out over 10 GB, deleted with one click, and felt great—only for everything to be the same two months later.
The problem isn't that you don't clean often enough, but that what you delete will grow back, while the part that's actually growing is untouched by cleaning software.
Cleaning Software Deletes Mostly 'Things That Grow Back'
Open any Mac cleaning tool, and the categories at the top of the scan results are usually these:
| Category | Typical Location | What Happens After Deletion |
|---|---|---|
| App Cache | ~/Library/Caches |
Regenerated when the App opens next time |
| Browser Cache | Chrome / Safari cache directories | Returns after a few days of browsing |
| System Logs, Temp Files | /private/var/log, /private/var/folders |
Continuously written by the system |
| Dev Cache | Xcode DerivedData, node_modules, Docker images |
Rebuilt on next compile or dependency install |
The purpose of cache is to trade space for speed. Delete it, and the App will be a bit slower on the first launch, then it takes the space back exactly as it was. This is the first reason for 'full again two months later': you are clearing a pool that refills itself.
This isn't to say clearing cache is useless—temporarily freeing space for emergencies is very effective. But if you want your disk to stay free of alerts in the long term, you have to look at another type of file.
What's Actually Growing Is the Stuff You 'Can't Bear to Delete'
Open 'System Settings → General → Storage', or run this in the terminal:
bash
du -sh ~/Pictures ~/Downloads ~/Desktop ~/Documents ~/Movies 2>/dev/null
Most people will find that the big stuff is never cache, but these:
- Photos and Screenshots. An iPhone photo is 2–5 MB, while a straight-out-of-camera JPEG can be over 10 MB; a
⌘⇧4Retina screenshot is a 1–3 MB PNG. A few a day adds up to tens of GB a year. - Images Saved in Chat Tools. Images forwarded in groups, materials from clients, work screenshots—received once, and a local copy is created.
- Downloads Folder. Design asset packs, wallpapers, images saved from web pages that you never opened after downloading.
- Assets in Work Projects. Exported design files, website
images/directories, App resource files—each project comes with a pile of original-size large images.
The common point of these files is: cannot be deleted. Photos are memories, screenshots might be needed someday, project assets are still in use. Cleaning software knows this, so they are skipped by default—so the part that's actually growing remains untouched every time you clean.
If You Can't Delete It, Make It Smaller
Since these images must be kept, the only remaining method is: reduce the size of each image without affecting viewing.
Most images are 'chubby' from the moment they are created:
- Cameras and phones use very high JPEG quality settings for safety, often carrying a lot of EXIF, thumbnails, and other attached data;
- Screenshots and PNGs exported by design tools usually aren't compressed or optimized at all;
- Images saved from the web are often never processed seriously.
These extra bytes take up disk space noticeably without looking any different to the naked eye. We conducted two public tests: 32,188 straight-out-of-camera JPEGs were compressed to save 76.8%; a batch of JPGs already compressed on the web could still save 46.8% (see the 'ImgZilla Test' series).
In other words, a 50 GB photo folder could easily free up 20–30 GB—and this space won't grow back.
Why Most People Still Don't Compress Images
Everyone knows the logic, but few actually do it. The reasons are very practical:
- File names change after compression. Many tools save as
xxx-min.jpgor export to a new folder; after compressing, you have to manually replace and delete the originals, making a mess of a large folder. - Dare not touch originals. What if compression breaks it? There's no going back, so you just don't do it.
- Online compression has limits and requires uploading. 20 images at a time, 5 MB each—personal photos and company assets aren't something you want to upload to someone else's server.
These three points are exactly what we wanted to solve when we built ImgZilla.
ImgZilla: Drag the Whole Folder In, Compress in Place
ImgZilla is a native macOS image compression tool that does one thing: compress images in place, nothing else is touched.
- File names, paths, and formats remain unchanged.
IMG_2034.HEICstaysIMG_2034.HEICand stays in its original folder; album organization and project references are unaffected. - Just drag in the whole folder. Automatically scans subdirectories recursively, skipping hidden files and
node_modules. - Originals go to the Trash by default. If you're not satisfied with a result, right-click 'Put Back' in the Trash to restore it. Confirm it's fine before emptying the Trash to actually free the space.
- Supports JPG, PNG, GIF, SVG, HEIC/HEIF, WebP, AVIF. Handles iPhone HEIC photos, screenshot PNGs, and WebP saved from the web.
- Runs locally, no internet required. Photos never leave your computer, with no limits on number of images or file size per image.
- Doesn't forcefully compress already small files. Files with a compression rate of less than 0.4% are marked 'Already Minimized' and kept as-is; it won't make images blurry just for a better number.
After compression, a built-in compare window (⌘D) allows side-by-side comparison and zooming in to actual pixels to check image by image—you don't have to just trust it, you can see for yourself.
Where to Start Compressing
It is recommended to follow the order of 'takes up a lot, low risk':
- Screenshot Folder (default on Desktop, or your custom location): PNG screenshots usually compress the most space, and there's almost no 'quality anxiety'.
- Downloads Folder: Delete the truly useless ones first, then compress the remaining images all at once.
- Your Organized Photo Folder: For example, camera imports or phone exports organized by year.
- Work Project Assets: For websites, Apps, and design export directories, compress them to make the website and install packages lighter too.
One place not to drag in directly: the 'Photos' App library (photoslibrary). It is a database managed by the 'Photos' App itself; modifying files inside directly can cause library issues. To compress this part, export to a regular folder first, or enable iCloud 'Optimize Mac Storage' and let the system handle it.
Also, two notes to avoid over-optimistic expectations:
- ImgZilla does not convert formats or change resolution. PNG stays PNG, dimensions unchanged.
- How much can be saved depends on the original state of the images. Images already seriously optimized won't save much—this is normal.
ImgZilla currently only supports macOS (12.3 and above) and can be downloaded from the Mac App Store. The free version allows compressing 10 images per day, and the quota is only counted for successful compressions—try a screenshot folder first to see the effect before deciding.
A Summary Table
| Action | Space Freed | Will It Grow Back? |
|---|---|---|
| Clear cache, clear logs | A few GB to over 10 GB | Yes, refills within a few weeks |
| Delete unused downloads, installers | Depends on habit | Depends on habit |
| Compress photos and screenshots in place | More photos, more space saved | No |
| Move large files to external drive / cloud | A lot | No, but access becomes inconvenient |
Mac keeps getting full not because you don't clean often enough, but because you keep clearing the part that grows back. Compress the images that are actually growing once, and develop the habit of compressing new images immediately—your next alert will come much later.