[Users] IMAP questions

[codejodler at gmx.ch]

Normally i'd happily do lots of test, but actually i'm under heavy load right now and i'm counting the minutes ...
Please excuse when i'm going on with questions, instead of reading things up :¦

If i move / copy mails from another account into IMAP folders, they will be uploaded to the server right.

(1) What does "rebuild folder tree" do in IMAP ? Are those mails copied over safe ?

I saved a draft with attachment. This is slow uplink here, it blocked claws for 3 minutes from working. 

(2)  Is it a good idea to configure "draft" folder in local mailbox ? Also for "pre-save messages" ?

I guess it doesn't make sense to configure "sent" and stuff to go local too since these operations will be done on-server right ?