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I am sure people have different reasons, here are mine.
First is grip strength/hand strength. I like for the kids to spend a few years developing hand strength, as opposed to just putting grips on. Advantage
Second is, I want the kids to actually be able to swing with rips and never think twice about it. I have seen and had kids in the past get a rip the night before a meet or worse yet during warmups and completely shut down. Currently (past decade) my kids don't even think about a rip when working out or competing. big advantage.
Third, getting a feel for the bar and learning to swing and execute tricks without the use of grips makes kids less dependent on grips and gives them a better understanding of the mechanics of swinging/ shifting etc... another big Advantage
Fourth, putting grips on a child too early in my opinion and in my experience can lead to injury. These kids have no idea how to swing on the bar and now they have a piece of leather in the way. Safety
Lastly and most important is peel factor, when you take into consideration that the four examples I gave you can actually cause a peel then you can conclude that a lower peel ratio is the result of spending at least a couple years with bare hands. This is the biggest advantage of all because a safe kid is a healthy kid.
Conclusion, the pain of a rip is worth a lower peel ratio and a well rounded swinger.