A battery grip for your dSLR is a good idea for a number of reasons.

As you’d expect you get greater battery capacity and a better hand grip, good for people with large hands like myself. Most battery grips will have a second shutter release button for easier use of the camera when held sideways.

This also comes in very handy when you need that extra little bit of height, as I did at my daughters school play the other night. With the camera held upside down I was able to take advantage of the cameras normally inverted periscope, giving me a better line of sight over the heads of the other parents without the need to get out of my chair.