BENEFITS OF USING A BATTERY GRIP

This picks up from the previous post on Focus Points.

There are at least four benefits to using a battery grip:

1. Using an accessory Battery Grip on your SLR can also aid greatly in being able to change focus points while shooting a vertical composition. Some Pro quality cameras have battery grips built in. The grips typically have additional focus point buttons and a shutter release to allow you to change Focus Points quickly without taking your eye from the finder. This is crucial for nature or any fast moving subject. Note that many underwater housings will NOT accept the addition of a battery grip as space is very limited.
2. Your shooting time can be extended as you can install two batteries at the same time. I can get an entire morning or afternoon on two batteries. Normally I'd have to change batteries after an hour or two. A distraction in the heat of great session.
   
3. Many come with a AA battery tray so you can use AA's in a emergency.
4. This one is subtle. If you put a grip on a Pro-Am camera like a Canon 50D, it now looks like an $8000 EOS 1Ds Mark III to the untrained eye. In other words, you look like a real pro. It has been said that wearing a camera is a license to explore. The battery grip can give you extra edge in getting "access" for better photos,i.e. credibility). Be careful where you want to brandish this appearance. Sometimes a little Canon G10 is better by being less intimidating.
   

The downside of using battery grips are the additional weight and bulk and the fact that you LOOK like you have a lot of money to invest in a REALLY expensive camera.