it doesn't really. it just lowers the air pressure going toward the bolt to power it. some may say since it does that, it saves you air because there isn't as much air pressure/force from the bolt hitting the ball. alot of high ends have low pressure regulators to cut the pressure the bolt has so they can shoot incredibly brittle paint for tournaments.
it's the build and the mechanics of the way the gun recharges itself. spool valves are always on the lower end because they're comepletely driven by air. they use air to shoot and blow the bolt back. poppet valves are always on the high end due to simplicity of a ram, hammer and hardly any orings to seal things.