My son did this his freshman year of HS. The way it worked for him was he was a starting pitcher on varsity and played position on JV. We are from Georgia like Dadofa17 and the rule is you can only play as many games as the varsity team plays, which is 26. It worked out fine because he only pitched on varsity and if JV had a game the next day, he just didn't play so he could rest his arm. The way it worked out for him is he got the best of both worlds. He got challenged on the mound and still got to work on his hitting and fielding on the JV team.
Of course, we had no say so in how this was done. This is the way the coach wanted it. Being on varsity, even if he doesn't play, it will give him valuable experience into the mind of the coaches and the pace and intensity in which the varsity game is played. There is a huge difference between varsity and JV and freshman games. You will get the reps in JV and freshman, but the intensity of a varsity game is well beyond what you can even imagine compared to the JV and freshman atmospheres.