Quote Originally Posted by Sean Setters View Post
1) The battery grip balances out the camera. It fits in my hands better.
2) The vertical shutter/control buttons make shooting in portrait orientation much easier.
3) Instead of having to keep up with an extra battery in my pocket, why not already have it in-camera?

Those are reasons why I've had battery grips on every single DSLR I've owned. Once you get used to shooting with one, it's difficult to go without it.
+1

To be honest, the integrated grip was a major factor in my decision to get the 1D X.