better shooting posture for portraits, additional battery capacity and the ability to take AA batteries should there be any emergency at all...
and it's very true of what synapseman said, not everyone is mature and knowledgeable enough to appreciate and understand it's not all about the camera sometimes, especially when it comes to paying clients, it comforts and assures them that the photographer they engaged 'looks pro' haha
it's also an image and professionalism
my 2cents and it really depends on usage,
gday guys