Sweat. When the winter starts to end you start to sweat again, and there's something special about it.
During the winter all the hard efforts, all the miles, they burn off your body fat and turn you into a lean cyclist. But during the summer, when you can sweat out pounds of water (pounds!), it is different than anything else. You are suddenly lighter. You have also dumped some body water that can be replaced with clean water.
It feels so cleansing to me.
But, before a hilly race or anything that has climbs at all, I believe losing water weight that isn't necessary to performance is a benefit. I don't think sweating immediately dehydrates a racer. Hydration of your organs and muscles is a separate thing, Eventually sweating obviously dehydrates the entire being, but eventually you just stop sweating and when you drink it refuels the important systems. After the race, you will be dehydrated though.
But to me, there's not much better than going on a long, hot ride and coming back with my face caked in salt and my kit ribboned with salt from dried sweat.
And then, obviously, to eat some party peanuts.