Power
Not all producers are going to be powerful. Some of them are going to be spineless figureheads who trust your artists' instincts. Some just want to see the radio play something a little better, even if it means finding an artist who that makes millions and seeing only a couple hundred fat ones for it. There's no shame in that.
But, if you're vigilant and successfully discover a few acts that really make it, you can establish yourself as what the industry calls "a big deal." The album's final cut is entirely in your hands. You think Miley Cyrus would sound better singing in Middle English? The new lyrics are "We thus cannot cease, we thus will not cease." You want Justin Timberlake to sound out of breath when he sings? Take a couple laps, Justin, it's for the good of the album.
You're in charge of the final product because people will trust you to make them the hottest thing since Hot Pockets filling. Music will be more or less determined by you. And you'll be invited to all the coolest parties. Don't let it go to your head.