I use Camelbaks for both road and mountain biking. A smaller one for road.

Advantage - disadvantage... biggest advantage is the ability to carry larger quantities of water and it's easy to access. I find I drink more when I have the nozzle right there. When I ride with a water bottle, I find it difficult to reach down and get the bottle and put it back. In fact, have dropped it a few times and am alway worried about looking down missing something ont he road etc.

Also you can carry just about everything in the pack, even the smaller road pack.

Disadvantages: Biggest complaint I hear, but it has never bothered me, is the weight on one's back and shoulders. Plus it's hot. The packs are really built well to distribute the weight and well, I think the pack actually keeps me cooler as I tend to sweat between the pack and my back. The sweat helps keep me cool.

Just my preference. I wouldn't ride without one.