For me, the greatest advantage of satellite radio is being able to listen to music commercial free. The main reason being that their main source of income does not come from advertisers, but instead from the listener.
Satellite radio offers over 70 channels of commercial free content with a pretty diverse variety. Everything from hip hop to heavy metal and now there even a Catholic talk channel.
Another benefit of satellite radio is the lack of static. You can basically drive from one coast of the country to the other and you will receive a strong and clear signal pretty much the whole way. The satellite signal is digital which insures its clarity wherever you go.
Another great feature is being able to identify what you are listening to you. The radio tuners receive meta data that includes song information like title, artist etc It's a great way to discover new music as you can simply scan the channels until you hear something you like, then you can see exactly what it is.
Unlike conventional radio, satellite radio is complete uncensored. This is the main reason why artists like Howard Stern chose to abandon their old radio gigs and establish their shows on satellite radio. It's great to be able to listen to music without those annoying beeps interrupting the vocals.
In addition to music, satellite radio also offers information about local weather and travel conditions. This information can be very detailed especially for the larger metropolitan areas. In the case of a natural disaster such as an earthquake which can knock a conventional radio signal off the air, satellite will always work and you can count on it for the latest news and information regarding the calamity.
So these are a few of the advantages that satellite radio has over conventional radio. To those that argue that the subscription costs money and conventional radio is free, I say this: Think of all the time you spend listening to commercials and scanning the dial for something you like and you will find that inexpensive cost of a subscription well worth the price.