In the days of film cameras, the add-on grip provided motor drive for faster advancing the film and winding the shutter, film magazines permitted 250' and longer spools of film for longer uninterrupted shooting. Modern dSLRs have fast advance even without a BG, and they shoot hundreds of shots without a BG. It is not difficult to merely carry a battery or four in a pocket, and swap them at a brief lull in the shooting. It is not difficult but a convenience having the buttons on the BG for portrait orientation, as photographers did without added buttons for decades. It is not a difficulty but a convenience in having more grip area, as again decades of photographers managed quite well with much smaller SLRs!
So do you need one, NO. Is it nice to have one, yes, for some.
True. About the only advantage of grip that I can see is that you can use AA cells in a pinch. I had, and sold on, a grip for my 20D. All my film SLRs had them to give me power advance.
If you think the grip helps you balance a big lens, you're holding things wrong. You should be supporting the camera by the balance point in the lens, not gripping the camera for dear life to keep the lens from pulling it down. Left hand under the lens to support; right hand on the camera to steer.




