It has a dial with 4 lines on it ranging from HOT to WARM.
I can’t think of any time I needed scalding hot tap water.
The dishwasher uses really hot water, I suppose.
I don’t want to waste money on needlessly hot water.
Thoughts?
go to a bath tub, with the water set to full hot and with a thermometer in the water flow, set the dial on the heater at a point that gives 110F at the tub. mark that point on the water heater for later reference. if you move the dial in coming to an adjustment then you need lots of time between adjustments, especially if turning it down, could do one measure and adjust each day.
A link for child safety says 120F, a link for most efficient says 120 F, so I’d guess 120F. 
I set mine there, but I wonder if I use more energy with a lot of hot water than I would with a small amount of very hot in the bath. I wonder how much energy goes into just keeping the tank hot, rather than heating water as it is used.
My dishwasher heats the water, but it’s still connected to the hot water line. I usually leave it on the lowest setting. However I have a desuperheater and a reserve tank coming off of the HVAC system, so my water heater doesn’t really do any work anyway.