Hi, first time caller- what is better for the cruise worker: Me handing out cash/leaving envelopes, or automatic gratuity?

I can’t get my head around the cruise company just keeping my tip money and using it offset the regular wage paid to the staff. Maybe I’m off there - does auto gratuity actually get paid on top of wages to staff? Or would it benefit most/all of them if i manually opt out of the charges and give cash/leave envelopes for folks i don’t see?

TIA!