[Dovecot] Quota problems with IMAP and POP?

Hello,

I would like to know if it could be appears problem using POP and IMAP in a mailbox? Is it adviced to use one of the two protocols?

My users use IMAP to see their emails (in the webmail) and POP3 to download their emails (in outlook/thunderbird).

Is it best to use the same protocol? POP and IMAP have the same quota engine?

Thanks.

-Nicolas