The official Gmail app for iPhone recently got a nice update, and in addition to a few bugfixes and performance enhancements, users now have the ability to save picture attachments straight to their iPhone (or iPad's) camera reel. That's a nice feature -- it means that you can browse and save attachments more easily.
I can imagine some nice use cases as well: You could grab an image from Gmail and put it right into a slideshow on your iPad, or send yourself some images from another computer, and insert them on to your iPhone or iPad's lock screen wallpaper easily.
The Gmail app in general is a solid app to have. Though I usually use the Gmail web client in my browser when I'm at home, and Apple's own Mail app when I'm out and about, there are times when I'd just rather have an official Google experience when browsing mail. With this update and a few others lately (the last update added support for Notification Center), Gmail makes an even better case for owning a spot on your home screen.