I use one for long rides. The backpack is big enough to pack a days worth of riding supplies, as all but one of my road bikes are not sporting a rack. My pack is designed to help keep my back from sweating(too much), but I still sweat regardless. I've been using a camelback type of device for over 20 years for multiple sports, and there hasn't been anything made that works any better for hydration since(IMO).

On hot days, I usually fill the bladder the night before and freeze it. I pull it out of the freezer a couple hours before the ride.