Aside from the egronomic benifits of a grip, my favorite advantage of the one I have, is the ability to use AA batteries. Old camera from the film days, the specialized battery was expensive and sometimes difficult to find. (some, mayby all) Canon grips allow the use of two rechargable camera specific batteries, or AAs. Likely the other manufactures do too.
|AF4_2483 Surfing the Serengeti by DaveInHouston|
from Hot Air Balloon view
|Peregrine Falcon by Psychic1|
from Best Wildlife Photo of the Week - 4