A slightly different lens that perhaps offers a little connecting ground between the views above....
I think for most of our kids, it's not so much that they need repetition (though there is a certain amount of "use it or lose it" in play). The basic concepts of decimals, fractions, exponents, whatever, are easily taught, and the usual endless worksheets of basic problems that grind our kids down in elementary school are a big driver to "accelerate, now, more, PLEASE!" Most of them clearly don't need more of this kind of repetition.
At the same time, what most of them don't get is practice using those simple concepts in complex ways. There's tons of hard things you can do with those easy math tools, and there's value in spending some leisurely time with competition math, AoPS, etc, to find them. Otherwise, I think what might happen is some kids end up accelerated not too fast, necessarily, but too superficially. They have a great big box of tools and they understand the purpose of each one - but they've never been given anything but practice boards to work on, and have no idea what to do now that they suddenly need to bring all their tools together to build a house. Or a particle accelerator.
