ok, with the 450d being relatively small, sounds like it could be a sensible addition as the one I am looking at has one already with it
A grip makes your camera look like the more expensive professional model that you wished you could afford.
Depending on the body (Nikon D300/D300s/D700), some grips only hold a single battery, and one battery is retained within the body itself (a silly design imo, but it means Nikon can use the same grip on 3 or 4 bodies, so I'm sure it makes sense to them).A grip hold 2 batteries so you get double the time between charges.
im not thread hijacking but can the shutter button on the grip work in manual, as in the one on the body could control shutter and the one on the grip can control aperture.
I haven't looked to see if I can configure one to ISO when using aperture & shutter priority modes, but mine are the same in layout.the shutter button on my pentax K20d and the shutter button on the grip - both take the picture. Have 2 dials on the camera - one for ap and one for shutter speed (in manual mode), in Av / Tv, can dedicate one to either one to ISO setting.
The grip also has 2 dials which replicate settings on the main body.
A grip makes your camera look like the more expensive professional model that you wished you could afford.
there lies the real reason for having a grip