The ground is required where there is a substantial amount of grounded metal and/or water around, such as bathrooms and kitchens, outdoors, etc.

Ideally, and legally, an inspector might want to see them connected. For interior dry areas, I wouldn't sweat it.

Having said, all that, I've recently read somewhere that the ground helps reduce static damage. Not sure where, but it wasn't by an "authority".

Larry
www.fineelectricco.com