I became a fan of using genuine Nikon grips when my Zeikos grip caused my D300s to stop shooting mid-session and had to be removed.
The benefit of a grip for me is the better feel and weight balance (especially with larger, heavier lenses) and when shooting portraits. Holding a camera 90 degrees counter clockwise with my hands at the 12 and 6 o'clock position gets old fast. And lastly the added frame rate I need when shooting certain events.
I've got Nikon grips on all of my bodies, I never leave home without them.