As a former college Volleyball coach, I implemented pool workouts frequently with my players throughout their 12 month training season. Due to the pounding that a volleyball player experiences during a long season, pool workouts provide a lower impact option for integrating plyometric workouts and jump training. We also used longer lap workouts for ESD (Energy System Development) and conditioning for longer matches. We used the shallower end of the pool to execute various explosive jump sequences for increasing explosive power in the lower body. Fewer knee problems and a higher vertical is a winning combination for any volleyball coach!
Other than strength training exercises that requires a lot of running, push ups and different kinds of exercises (and also requires some additional equipment using jumpsole and more), pool workouts are essentially good for athletes in order for them to lose weignt, tone up muscles, prepare for the race and increase stamina. very recommended in every sports indeed.
As a volleyball coach I implement pool workouts at least one time in two weeks. I find it very effective because it provides different look on training and the players like it. Usually I give them low body plyometric drills which will improve their jump ability, or ask them to swim around 500m which will improve their VO2max. Also, players that are slightly injured would be relaxed and will recover better. :)