You’d think these heavy digital SLR’s don’t really need any more added weight, and you’re right.   And do they really need to be bigger?  Well it depends.  As a Canon owner (5D Mark II, 40D, 20D) with a variety of large lenses, I have found the battery grips to be very helpful simply because they give you a more substantial surface to grip when there’s a big lens mounted.  Plus, when you turn the camera vertically, like when shooting portraits, you can still have the shutter release button on the top because the grips replicate this button for you!

The extra battery power is a great added plus.  You can shoot all day with a battery grip!    The added power, the more substantial grip, and the better balance of the camera when mounting a large lens, all make these little gadgets a great add-on!