“Whether you read or write your email on your phone or on your desktop, changes you make to Gmail will be seen from anywhere you access your inbox.” [What’s new on Gmail?]
Plenty of you use client email applications on your home computers with Gmail — Apple’s Mail, Microsoft’s Mail or Outlook Express, Mozilla’s Thunderbird, etc. The downside as been that, so far, your email client could only retrieve messages from Gmail via the POP protocol. Any changes made on your local client — deleting messages, moving them into folders, etc. — weren’t reflected back on the Gmail web interface. If you needed to check your mail from your office, a hotel kiosk, or a friend’s computer, you wouldn’t get exactly what you may have been expecting.
IMAP has several advantages, including letting your email program have a full, two-way conversation with Gmail so that your email organization can be the same regardless of your viewing method.
That’s what’s known as A Good Thing.