Yes I’m sure the gains are small. I personally don’t work on BMW I am a HD diesel engine technician. They do lots of small things that do add up. It’s also for cold start emissions to get the engine to temp as fast as possible too. Lower pressure has been lowered on newer engines for less of a parasitic draw too

Yeah it’s for parasitic draw, 2 speed water pump with a solenoid and speed sensor. If the water pump doesn’t need to be on full blast it can be slowed to allow lower parasitic draw on the engine and improve fuel economy