They say clothes make the man/woman. In our business, music makes the brand. And let's be honest, if someone is driving along in the car and hears music that "feels in sync" with who the consumer is, they'll turn up the radio and lock into the brand. Seems so simple really.
But, as anyone who works with music overlay will tell you, it's not that simple. Music is such a tremendously personal thing. You can't be all things to all people. Music is what makes people feel unique. If a song is perceived as "selling out" or "corporate rock" certain personality subsets tune out.
If the arrangement is too strident it alienates certain demographics or psychographics.
The most successful campaigns decide specifically who they're going after, and choose music appropriately.
Being all things to all people when it comes to music choices for advertising, is the equivalent of taking a beautiful wine and adding water to stretch it out. You end up taking a mind blowing experience and watering it down to a limping shadow of what the campaign could have been.
Top brand professionals subset their approaches and create specific, targeted advertising to reach one target at a time.
Geico does this very successfully choosing MTV style ads to hit the young motorcycle crowd.
Here's an article that expands on the topic.