A cleaner is only useful if you trust it, so here are the rules SpaceUp Mac follows:

- Nothing is removed until you see what it is, why it's safe, and approve it.

- Your own files go to the Trash, so you can undo.

Hi, I'm Irshad, the maker of SpaceUp Mac.

When I ran it on my own 256 GB MacBook Air last week, the biggest surprises weren't my files. They were Xcode DerivedData (5.71 GB), Gradle caches (5.05 GB) and an iOS Simulator runtime (8.34 GB) I'd forgotten about. Most people only ever see a gray "System Data" bar.

So I'm curious: if you've ever cleared space on a Mac, what was the biggest thing you found, and did you know it was safe to delete?

Your answers help me decide which folders SpaceUp should explain next. I write a plain-English page for each one at spaceupmac.com/folders/.