What is the difference?
When you use IMAP you are accessing your inbox on your mail server. IMAP does not download messages onto your local computer. Although the messages appear on your computer while you work with them, they remain on the central mail server.
POP does the opposite. It checks the server for new messages, downloads all the new messages in your inbox onto your computer, and then deletes them from the server. This means that every time you use POP to view your new messages, they are removed from the mail server.
IMAP makes it easier to view mail from multiple device
Because IMAP leaves all of your messages on the server, you can view these messages from any location with Internet access. This means the e-mail inbox you view from home will be the same one you see at work.
Since POP downloads new messages to your computer and removes them from the server, you will not be able to see those new messages on another computer when you check your inbox. Those messages exist only on the computer that downloaded them using POP.
You may want to keep local copies
While using IMAP to save e-mail on the mail server is recommended, there are reasons to have local copies of messages (messages downloaded to the computer, as with POP). Fortunately, IMAP allows you to keep local copies of all your messages. You may want to download your messages, then disconnect from the Internet and work with your mail offline. Please note that while you are working offline, you cannot send or receive mail. You need to be connected to the Internet to do those tasks