A label will often pay to record your music, including hiring the best producers or session musicians, getting other established artists featured in your songs,

A label will often pay to record your music, including hiring the best producers or session musicians, getting other established artists featured in your songs, getting the best people to mix and master it to make it sound great. Then they pay to market it and put it on the radio (which is just one big ad network these days). Really it's very similar to raising venture capital. You don't need to do it, you can bootstrap a company with almost no money and people do it all the time. But if you have the chance to work with an expert who's willing to put in a lot of money upfront, it can really accelerate your trajectory.