Using POP or IMAP depends on how you want your email to work for you. Both are email protocols and work differently: POP is the simplest and IMAP is more modern and has more capabilities.
Any email client – and by that I mean the program you use on a PC or a Mac that is not web-based email – will offer either POP or IMAP as a choice. So POP and IMAP aren’t unique to Apple Mail.
The difference between POP and IMAP is this: POP stands for Post Office Protocol, and when an email program (like Apple Mail or Thunderbird) is set for POP, the program downloads your email and you work with it on the PC or Mac. You compose email and then your computer only talks to the mail server when you click “Send” or “Get Mail.”
With IMAP, your email client works with email that stays on the server. Your email client is in constant contact with the server, and when you compose an email, your work is immediately reflected on the server. IMAP leaves all mail on the server, unless you specifically delete it from your email client.
There might not seem to be that much difference, but IMAP really comes into play when you want to access your email from more than one computer, and because IMAP leaves all email and drafts and sent mail on the server, you can access email from different computers and see the same email.
So POP is simplest if you have one computer, and IMAP is more capable for more options when using email. When you set up Apple Mail, you can decide which way you want to go.