Our shower handle had a governor like this that we were SO happy to remove.
We keep our hot water heater at a reasonable temperature to prevent bacteria growth, but we kept having to turn it higher to get even a reasonable amount of hot water in the shower (and wasting a lot of water waiting for it to turn off).
When we finally figured out how to disable this, we were able to turn the hot water heater down just a bit, and now we only have to wait a few seconds, not a few minutes for the water to be hot enough to hop in. If we want burning hot water we could have that too, but it is no longer necessary to turn it all the way up.
For over a year we were heating our water at the water heater, and then cooling it before it was delivered in the shower. What a waste!