Regarding 3and2, I just retired 
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It is a tough balance for most HS's. A coach is certainly responsible for protecting the health of his players. A coach is also responsible for putting his players in the best position to win. P, SS and C are the most important positions, requiring (in most cases) the best/strongest arms. SS and C are the most difficult to balance as P's - especially C as others have noted. The average HS program has a limited surplus of guys with strong arms who are able to man any of those three positions effectively. The scenario that puts the team in the best position to win quite often includes a properly managed solution that allows those players to be 2-way. Yes, it is also the responsibility of the coach to develop enough talent behind these guys that can step into those positions and negate that scenario but often, the "potential talent" and depth pool just isn't there. Subsequently, going down the depth chart would have significant impact on putting the team in the best position to win. Large programs with depth of talent and arms have more viable options.
Proper management and as much development of others as possible is key. Or, retire, I guess 
. As others have said, this balancing act happens far more than most realize. Not easy. No perfect solutions. No matter which way you go, you will be criticized.
Tying this back to the OP... we used a similar approach, whether it was protecting a C who may be a 2-way or just general preservation of a C arm (i.e.- during a tourney or a cluster of games due to schedule changes). I would have my C make a strong throw down the first inning always. This would often set the tone for opponents deciding not to run much. Then, go easy the next few innings and go strong again somewhere in the middle if he hasn't made any game throw-downs. Keeps him sharp, preserves the arm, and keeps opponents honest. It's not that it's just seven throw downs. It's cumulative, particularly when talking about multiple games in a short period of time. Warm-ups, bullpen throws, game throws, throws back to P, etc. BTW, we also had other methods to reduce some of these other throws for the C as well.
PS - there is certainly merit to Dominik's statement as well. The ideal pitching motion and the throw of the catcher are typically quite different. This also has to be factored in. A whole 'nother conversation.
Also, I should add... over the years, the two C's who continued to balance P/C duties under my watch in HS went on to play in college, one as a P, one as a C. Both have healthy arms to this day. Ability to hit a well placed college CB is where I failed them 