What are the differences of Gmail?
Gmails can be accessed via IMAP or POP if you use a mail client. POP doesn't make much sense as explained in the section about IMAP basics.
The browser based Gmail has Labels. Each mail can be labeled with multiple labels. This solves the age-old problem when a mail belongs to multiple categories. This doesn't fit to the Imap mailboxes where a mail can belong to only one mailbox. Even the Inbox is a Label. As a result mails can be downloaded once for each Label applied to it.
Gmail has a quite different archival concept. Archiving Gmail style just removes all Labels from a message which removes it from all mailboxes.
Benefits of Gmail
It doesn't cost anything. The storage capacity is good.
Drawbacks of Gmail
You get obnoxious advertisements when viewing Gmail via browser. Nobody has any clue what Google does with your email data. The concepts of Gmail don't fit 100% to the Imap ones. As a result mail may be downloaded multiple times to the computer.