It's just about the same. The real advantage of making a standalone webcam for me was because my laptop's camera is just above the keyboard and unusable in most scenarios.
Considering the pi needs to be powered over one USB port and the other USB port is used for data that makes two wire hanging around: ts that really better than an USB webcam then ?
The Pi can be powered from the same data port so that it only needs one cable. If you're comparing this project to an off-the-shelf USB webcam, also consider that a Raspberry Pi makes for a very hackable base (for example, I'm planning on wiring up an LED ring to it sometime soon).
