It's all about depowering the scrum. Personally I don't think it's safer (the Bajada scrum packs using this technique), but that's the IRB U19 law variation as it exists. As mentioned in a previous post - I think NZ have a dispensation on this law in their juniors, although I'm not sure at what age it starts.
Safety obviously needs to be the paramount concern, although I'm sure this could be managed in Australia, even if it meant an extra module in SmartRugby for coaches of players from u15 up based solely around the scrum, as well as improved referee training (I've seen some awful examples of poor refereeing in junior scrums where the scrum was unsafe because the ref didn't understand the scrum)
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