yes, they don't help much when you're crossing the Nullarbor.
Still, they are handy in the early stages of training to help students get the concept of distance/time/ETA/groundspeed checks etc. I find ten minute markers a bit easier than six minutes, ( always had trouble with that six times table) working backwards from the destination.
IMHO its simplest to use minutes as a common denominator for everything rather than some things in litres, others in miles etc. But theres lots of different ways of doing it, and they all achieve the same result, like the whizz wheel.
------------------