The shower systems. The pumps. The Mira thingy. It serves no purpose I can understand in my own context.
Get you now!
Ours is to boost the pressure and give a constant temperature so you don't get burnt or frozen when someone turns the kitchen tap on full.
We run a low system pressure, esp upstairs, as the open tank is in the roof about 2 meters above the shower.
We're about 4 miles from the waterworks and a similar altitude so would never be able to run a shower off mains pressure.