Good practice makes perfect. Bad practice reinforces bad habits. I'm a proponent of shorter quality reps. There is no benefit to tired sloppy techniques. This is why in other sports, like baseball, players don't take batting practice for hours on end. It's much more beneficial to swing / kick properly to train muscle memory than to let your muscles remember a sloppy technique resulting from a long tired workout. Better to workout more short periods than fewer long workouts. Endurance is a different animal. There are many methods to increase endurance but science shows that HIIT training is more effective than long workouts at medium - high intensity.