Each month, I archive all the contents of my main gSuite account to a third-party repository. I do this via an IMAP-based transfer.

Unfortunately, when you use an IMAP-based transfer to move files, Google doesn't actually delete the emails from your gMail/gSuite account. No, it simply removes all labels from them. This means that instead of getting space back – space that Google charges for in gSuite – the messages simply become not-easily-visible within gMail. None of your space is freed up and, thus, space-charges for those unlabeled emails continue to accrue.

Discovered this annoyance a couple years ago when my mail-client was telling me I was getting near the end of my quota. When I first got the quota-warning, I was like, "how??? I've offloaded all my old emails. There's only a month's worth of email in my Inbox, Sent folder and my per-project folders!" That prompted me to dig around to discover the de-labled/not-deleted fuckery. So, I dug around further to find a method for viewing those de-labeled/not-deleted files. Turns out, putting:

-has:userlabels -in:sent -in:chat -in:draft -in:inbox

In your webmail search-bar will show you them …and allow you to delete them.

My gSuite account was a couple years old when I discovered all this. So, when I selected all the unlabeled emails for deletion, it took a while for Google to actually delete them. However, once the deletion completed, I recovered nearly 2GiB worth of space in my gSuite account.