bballman - Understand, but for workouts, the little squirts had to do this.
I am nowhere near the top levels of baseball and do not know why folks want to swim other than as Bishop said for conditioning. If a kid is only looking for aerobic conditioning/stamina, then they can do it without arms.
I had thought that swimming would be good for my boy if he continues in baseball because it works the heck out of your body and can be used year-round. Then I read that a lot of swimming can be hard on shoulders so I thought maybe not, except as I have described.
As I have posted several times, bleachers are a very good workout. Go hard for two or three minutes, rest for 30 seconds, repeat until you are heaving. Gym bleachers in the winter if there is ice outside.