I’m not sure I would call it a ‘must have.’ But it is an upgraded choice with an upgraded price tag. The primary benefit that I see is if you’re the one most often using the shower, once you find you temp sweet spot, you can just leave it there. Every time you turn the water on, your temp is ‘saved.’ Versus a pressure balance valve that requires you to find the right temp every time it is turned on. And, as you said, you know what a volume control does - it allows you to adjust volume - turn it up to rinse your hair, turn it down to save water while lathering up if you want, turn it back up to rinse. It buys you flexibility.

Thanks for these considerations. Actually really helpful in understanding the practicality of the additional option!

I prefer thermostatic, but if you don't prefer that function then there's no need to pay for it.

It isn't really a must have, but I love the functionality of it. We have one in our guest bath and installing one in our main bath remodel. We don't have one at our weekend lake home and I get annoyed that I have to adjust the valve to get the water temp "just right" lol.

I have the thermostatic controls in my master bath but mine doesn't have volume controls because I am in California 😂 I do have a three way diverter which enables me to switch between the shower head and the two hand held shower heads I have - in California you can't have more than one water source at the same time.

I could be wrong but in addition to the benefit of not having to adjust the water temperature every time I think there is also a benefit if you have the kind of plumbing where flushing toilets or running water in other places causes shifts in the temperature of the shower.

I do have the pressure balance valve in the guest bath because no one using it would need to "save" the temperature. It gets used so infrequently that I have to remember to periodically run the shower or else it starts smelling from the sewer gas because the water in the trap has evaporated.