There's actually a very tiny advantage for the enemy if they can hear the music; if they are familiar with the skin, they could hear the differences in the music and know which skill Sona leveled first.
They may also be able to take advantage of Sona players that like to switch forms shortly before engaging in a fight. This could inform the enemy that she intends to go in, even if they can't see her yet, and could therefore affect the game in a way normal Sona would not.
It's extremely minor, and the second example is entirely the Sona player's fault, but the issue is still there.
https://i.imgur.com/1HvNiEO.png?noredirect