IMAP allows you to directly read email from the mail server opposed to downloading all the messages that are unread. IMAP is great to use if you plan on checking your email from numerous computers, but keep in mind it does require an active internet connection while reading your email. Also note email stored on your account does count against your overall disk usage so if you are concerned about disk space this may also not be a good feature to use as POP3 will delete the emails by default once you’ve downloaded them to your email client.