Power
As a studio musician, you're pretty much at the mercy of those who hire you. If they want it played fast, you'll play it fast, even if you think it should be slowed down. If they want nothing but the highest notes that your instrument can make, you'll play those notes without a second thought to how badly your ears will suffer. If they want to add a Norwegian folksy feel to their punk rock song, by golly, you'll give it to them.
If you're established and in demand—by which we mean totally overbooked and everybody wants you, then you will have the ability to say no to a project. Barring that, though, you'll be at the mercy of your employer.