Problem with imap it seems to me is that it will tend to add to my usage each time I check messages whereas pop maintains the message files on my computer. I have an allotment of ViaSat usage for the month and have to pay for extra, it is already expensive, but all that I can get in this rural location, and it works well including their voip phone service.
not sure I understand.. IMAP only downloads new messages. If you want to make sure you only get new ones, create ( or use) your local folders and move all gmail emails to local folders everytime. That way they are on your computer. I just use filters to filter all emails to specific folders, or delete junk.