email: when to import, when to archive?

I’ve read the manual and searched the forum, and I’m still not clear on the difference between importing and archiving email.

I’m trying to clear out Apple Mail, so the idea is to get all my “filed” emails (some 30,000!) into DTP (with an .mbox backup) and delete them in Mail. I want to retain the folder substructures. Do I use Import or Archive for this?

Archiving is recommended in this case as it adds the selected mailbox and its submailboxes to the group “Emails”.

Importing adds the selected mailbox(es) or selected message(s) to the current group but without submailboxes.

Thanks for the clarification!