What I think G-Flex means is that an effective power storage flywheel is a little grandiose. Unless it is perfectly balanced, a medium sized flywheel won't give you much in terms of revolutions. Since the dwarves would likely use stone to make their flywheels, we're talking something large to do maybe not much at all.
So a potter's wheel would be practical application, when we get pottery. It'd be like making a mill: you make a stone flywheel at the mason's shop, some kind of bearing at the forge, and need 1 unit of wood to make a pottery workshop.
I digress. The only other use I think of for a flywheel would be regulating a complex machine's rotation, or keeping something rotating if it has an intermittent power source. For instance if, say, wind was implemented to be more sporadic so windmills don't generate power all the time, then you could add a LARGE stone flywheel (3x3) to the machinery underneath which would keep it going providing power at a decaying rate until the winds pick up again. The flywheel would, of course, drain a lot of power from the windmill from a rest state (say, 30 or 40), then draw less and less until it got down to a paltry 1. Until the power runs out.
You could, of course, prime the flywheel with dwarf power. For simplicity, if capstans were implemented, building one out of stone could be a flywheel whereas a wooden one could be a capstan and a metal one a winch. Only the stone one would work as above, the other two could be ratcheted (flywheels can rotate free, capstans and winches only rotate when driven). Then you have period components that happen to behave in a useful manner.
And crazy little buildings that have four dwarves on then spinning around like mad!
PS: Bricks, fantastic meta-game observation!