Those high c/u's can sure take a long time to reach the plate when you're coaching.
Yet my son will occasionally throw a high c/u. I have seen some mighty whiff's come from that, as the batter thinks he is getting high heat for Christmas and swings for the fence.
And sometimes he will throw it such that the batter thinks it will be a fb above the top of the zone, but it drops into the zone at the last second for a called strike. Risky? Yep. But any pitcher who doesn't want to take a risk shouldn't take the mound. And sometimes that fb aimed low & away misses over the middle.
Coach L is correct that the c/u doesn't have to have movement. But late movement makes any pitch more effective.