Battery Grip Function for your camera
Its primary function is to increase battery capacity.a secondary function is to relocate some controls onto case so you have similar controls to hand if turn the camera through 90 degrees.it has another function that allows the photographer to get over lousy ergonomics by adding more space to grip the camera.some allow you to use standard batteries (such as AA's) so that you can continue to take photo's once your batteries are exhausted as you can buy more batteries from shops.
if you are a professional photographer then the battery grip may make sense.if you are a prof wannabe, or you want to be 'seen' by others as being a pro then a battery grip can be the all important kudos bit.. but you are deluding yourself.
the battery grip design and layout dates back to the old days of motor drives on film cameras. it may have been important then.. it isn't any more.if you bear in mind a modern dSLR battery should be good for anywhere upto 300 to 600 images and apre batteries are cheap and lighgtwieght, why lug the extra weight and bulk around. (natch Nikon & Canon owners (cos only Nikons and Canons are used by pros!) do feel the need to carry uneccesary bulk around).
if you look at photos in the LCD display a great deal then that may be a reason to increase you battery capacity, but otherwise y'don't need it.alternatively if you are away from a recharge point it can be a godsend to have an alternative power source to recharegables.
