Here's why:
- You can access and modify your email from web, phone or local computer applications and have the changes synced automatically.
- It's faster and more efficient to access emails and email headers.
- Folders are synced between the server and all clients.
- Move an email to a folder and it gets moved everywhere.
- Most popular email clients support IMAP.
- Emails can be copied between server and locally very easily using drag and drop (even large volumes).
Do it, do it now. Or when you've got a few hours to kill. You won't regret it.