Hold music is part of a good customer service model, demonstrating to callers that you care about making their wait a positive experience. It boosts your professional image and increases credibility, particularly when using custom messages …
Whether it’s when being transferred through to someone else, or simply waiting for the correct person to become available, being on hold presents a marketing window of opportunity to sell additional products and services, enhance your branding efforts, offer a more professional image or provide helpful information.

Of those businesses that responded, 85% would recommend on hold messaging and believe it's a useful marketing tool that adds value to the business. They rated on hold marketing as effective as Internet, TV/Radio, Direct Mail, and Print marketing.
If it is a genre, hold music, it's fair to say, is a troubled one with few hits. It's not really meant to be loved or even listened to — it's meant to communicate something specific: Don't hang up. (Cornell makes this plea specifically at the end of his song.) Silence is believed to be a death knell for phone calls — people will simply think the line is dead and hang up. This is true even on non-hold calls; it's why phone companies transmit something called a "comfort tone" over phone lines, a barely audible synthetic noise that signals a connection is still there.