Is it safe to delete app containers?
Your data Only if you're sure.
A sandboxed app's settings and documents. Removing it resets the app.
Where it is
~/Library/Containers
What “Your data” means
This may be the only copy of something you care about. ClearMac never pre-selects it, and moves it to the Trash only if you choose it yourself.
How ClearMac handles it
ClearMac lists it with this label but never pre-selects it. If you choose it, it goes to the Trash, so you can put it back until you empty the Trash.
This page is generated from the same rule ClearMac uses on your Mac (library.containers), so the app and this page always say the same thing.