Is there any value in sizing windows to match the block heights? For example, would it save on labor and/or reduce waste?

sure, there may be a value based on labor, but if its a one-off house, why not design it for looks? Think about it this way, you need certain size windows for egress, which need to be a certain min from the floor...that window sits in a buck, of some sort, so the buck exterior dimensions has to work the block hgt, so typical requirements would be in 16" or 24" increments, depending on the block used.

As you can see, you could work ALL your increments to full block hgts, but what about at say kitchen counters.....now the window could be as much as 15" ABOVE the counter top, else it may be 2" below, etc, etc...

I wouldn't beat the window sizing detail to death, because a lot of cuts are used in other places, and the bottom and top cuts are for the window width, !

Also if you are using reversable blocks the top and bottom cuts can usually find another place to fit in as well such as another window opening. It all takes on-the-fly planning as you go to minimize waste.

As Jim pointed out if it's a one-of house put em where you want em

Generally speaking the lentils for the windows are determined by the door lentil which is not adjustable. That is if you like your trim to be all at the same general height.

Dave