A few years back somebody on here linked a study (in Canada if my memory works that well) about feeding roosters Layer feed. The conclusion was that if roosters are fed nothing but a feed that contained the same amount of Calcium as Layer they sometimes could, possibly, might have issues with internal organs. The study did not show that each and everyone male fed that duet had issues, some did not. Even on those affected, it usually did not kill them, but damaged internal organs so they were not as efficient as they could be. It can kill some but I think if it more as my liver from when I had Hepatitis B in 1987. My liver is scarred as confirmed by a scan. My doctor is very cautious in prescribing certain medications because of that. Sometimes I have to get bloodwork done. Damage does not automatically mean instant death.
From that study on roosters there is a risk in feeding non-laying members of your flock a feed that has the amount of calcium in Layer. There are studies that show that feeding growing chicks that level if calcium also can, possibly, might cause issues. With growing chicks it is more serious than with adults. I strongly recommend against that.
But there is a second side of this. It is not how much calcium is in one bite, it's how many total grams of calcium do they eat in a day, and that is averaged out over a few days. If your chickens forage for a lot of their food the total amount of calcium they eat in a day may not be that high. If you feed a lot of low calcium treats they may not be getting that much total calcium. If you feed a lot of low calcium treats there may be other nutritional issues but that does reduce the risk from calcium.
For me the answer is easy. I almost always have immature chickens in the flock anyway so I never feed Layer although my flock forages a fair amount. I feed Grower to all of them with oyster shell on the side. The ones that need the calcium seem to know it and the rest don't eat enough to harm themselves.