Coach May,
In general I agree with blocking everything and always protect the blue in all situations. The catcher is always going to try to block/pick/smother every pitch. Always, no exceptions. Never is free rein given to ole' a pitch and let it go to the backstop. It's never "I don't need to block this pitch" but rather "How am I gonna stop this one"... those are the pitches way off the plate.
The catcher's stance dictates everything he will be able to do unless he is always in a runners on base stance. Then his blocking range is wider but if he down low (butt fist-high off ground), he is limited to what he can do laterally.
The issue isn't blocking but when should you block versus pick versus smother. And that actually boils down to pitch recognition more than anything. By HS, if a catcher doesn't block well he isn't a catcher for long. Blocking hurts, period. At 85-90 mph, even the pitches you block fairly well ding you to some degree. The further up the ladder a catcher progresses, the smarter he has to be about protecting himself because the season gets longer. Show me a catcher with no bruises after a game and I'll show you one that sat on the bench.
The pitches that I don't advocate blocking are the ones I described that are in a different zipcode. 18"-24" off the plate is at the outer limits of what can be blocked...realistically, our college pitchers (most were 85-90 mph) were given a zone 13 baseballs wide at the plate that they knew the catchers should block 100% of the time. Get outside that and they caught hell from the coach and the catcher. Speed doesn't bother a catcher...a pitcher with no control of anything does.
Basically the zone is as wide as a normal door, not a difficult target even for a 12 yr old. Plate is 7 balls wide giving you 3 on both sides...catcher sets up 2 balls outside, you have a 1ball/7ball/5ball zone with the 5 balls being to the side the catcher set up. Any HS pitcher should be able to do this easily..if not, either his mechanics are way off or he is badly losing focus; either of which demands a quick visit from the catcher.
MLB catchers as good as they are don't block a pitch 2 feet outside...they pick and hope to knock it down/smother it. Many HS coaches go overboard on the blocking everything to the point of wanting catchers to dive for ball even with no runners...really simple reason is they see the pitch from the side (vertically) not from behind (horizontally) when in the dugout. For that matter, there are HS coaches don't know how to watch a catcher recieving a pitch to tell pitch location.
How often have you heard a HS coach tell a catcher to always protect himself...probably only if he caught himself. Back in the 60's/70's that was the first thing that came out the coach's mouth because you can't help the team injured. You can play hurt/dinged and be effective (normal catcher status at some point) but being injured usually limits you too much.
All goes back to pitch recognition which is why it is so important that catchers do bullpens and work hard. Bullpen sessions give a catcher a look at all the pitchers,their deliveries and their movement.