Actually it doesn't save them anything, in fact using densified propellant where it's not actually needed to get sufficient performance for the mission (i.e a ISS launch) will cost more in fuel as SpaceX always fully fuels the rocket even if all that fuel is not needed (provides margin in case of issues and for landing the rocket)
Arguably it'd be riskier to use non densified propellants for these missions as then they'd be using different procedures than the cargo missions they launch regularly and will have less experience with it and opportunities to find and fix any issues on a cargo mission before it affects a manned one.
The benefit is for satellite launches, the increased performance allows for launching heavier satellites.
It's highly debatable if there is a higher risk to human life as well - unlike with rockets where you fuel up before the astronauts board, you don't have people approaching a fueled up rocket which could explode with no possibility of escape. Instead if there is a issue while fueling up, the astronauts are in a capsule with a escape system which should pull them safely away from the rocket if there is a problem.
Arguably it'd be riskier to use non densified propellants for these missions as then they'd be using different procedures than the cargo missions they launch regularly and will have less experience with it and opportunities to find and fix any issues on a cargo mission before it affects a manned one.