I have ALWAYS thoroughly groomed my horses after a ride, or even after ground work; to me it's the best way to tell if there are any sore spots, and it quarentees that all sweaty spots are thoroughly 'removed' if you will. I will hose down\shampoo as necessary. You can do it while they are eating their grain. I always allow for adequate cool\dry off time, well before I reach the paddock, so when I get there, I can focus on grooming, and making sure the horse is 'okay' after the ride.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."