Offload app vs delete app confusion

I read that ''offload app'' means ''free up storage used by the app, but keeps its documents and data. Reinstalling the app will place back your data....''

Delete app will delete the app and all related data from the iPhone...

What's the purpose, really, of the first if for instance I wish to keep Facebook but want to ''offload'' the content that uses space on my iPhone. App size: 250 MB. Documents and Data: 4.73 GB....

Is there a way to wipe out data which I could find back if needed on FB but free up space on my iPhone?

How to offer useless ''options''....