[mindnoise]

well let´s say 99%, safe

a region is NOT an audiofile or midi take, it´s just a ´marker´ for a selected chunk within a physical existing file.
You have two options:

1.delete unused regions
2.delete unused regionsexcept audiofiles

First will remove or delete everything, remember when your REMOVE files these are still in your session folder
second will leave your original audio untouched whatever you do. just the ´slicing´info will go.
As a definition: Unused is ERVERYTHING that is NOT in the Edit window.
And will not affect playback.

If you are unsure you may can first "Save a Session Copy" (file menu) in another place and then start cleaning your the session of your choice.

hope this helped
best