The only place where I can see an embrittlement issue on an action would be when an action had been recased several times. Not common, yet. Most recasing soak parameters are necessarily well within range.
At the met lab sections are routinely cut, polished and reviewed. Case depth takes time. Non-linear time. So, excluding the multi cased action, there is considerable leeway, within the conditions normally used, trained in, and passed along. In cases like these,where destructive testing isn't possible, you just want a procedure that keeps you between "too little, and too much".
Not everyone is comfortable just doing as they are told. Some of us like to know exactly what the range is we can get away with, and what effects our little flourishes leave behind.
Some believe in magic, some in science. It's all good.
Very well said CZ.....
Best,
