I know the answer to this has to be on the forum but after multiple searches, I couldn't dig it up:

I recently had a new faucet installed. It's working fine except that the water pressure is ever so slightly lower. I checked the aerators and rinsed them out. Looking under the sink, the new shutoff valves are straight up and down. I haven't checked them yet to see how much more I'd need to turn them to open them up completely because I'm unsure if it's all right to open them up completely, which would probably solve the lower water pressure. I remember reading somewhere that you open them completely but then back off a quarter or a half turn so they don't stick in the open position as scale builds up.

How far should the water shutoff valves for a sink, tub, or toilet be opened?