"purge storage"
on the storage page, what happens if I hit this button? I'm scared to try, out of fear that I'll lose everything. It says next to it, "Purge files from personal library." What I'm wondering is if that's automatic or (hopefully) I hit it and then get screens with guidance where I can select what to keep and what to delete? Thanks.
Purge storage clears out all files synced to the Zotero server on the server (it doesn't delete them: they're still there locally). There are very rare occasion's when you would want to use it; the only ones I can really think of is if you're switching to webDAV syncing for your personal library or if you want to stop syncing files for your personal library (and want the space for syncing group files, say).
(Technically "Purge Storage" would free up space temporarily, but you'd have no control over when local files were re-uploaded and just filled up the quota again.)
But speaking from personal experience, I find the lack of hassle and ease of use well worth the max. 10$/month file storage costs.