Originally Posted by Pikachu_Two_Trainer
you mean the radio? It wakes the snorlax when you play it
It has more uses than that.
If you set it to Pokémon March, Pokémon will appear more often. Setting it to Lullaby will reduce the the chance of running into them (much like Repel).
It won't effect what Pokémon you see, but it will certainly effect how often they appear.