Power
In theory: a lot. You're responsible for making sure customers get the correct prescriptions, thus giving you a ton of power over them. They come to you, ignorant of pharmaceuticals, and you can get them the proper medication (the one that their doctor prescribed) that will hopefully ease what ails them.
In practice though, you're more or less powerless. Customers yell at you, the insurance companies boss you around, and you need to rely on the pharmacist for direction. So yeah—not a lot of power.