Is Sound Necessary?

I have a paid toon, but I mostly play my Froob accounts and generally just do missions with them. I usually turn the sound off and listen to my own music.

Are there any important cues or other sounds key to game play in missions that merit turning sound on? I don’t recall monsters giving off any tell tale sounds that might alert you even if they are out of line of sight.

Sounds provide clues when a mob is chasing or attacking you.
You can hear sounds of battle in adjoining rooms.
The music does change as well, just like in a movies.

However, I do turn it off when others are around because I suspect it bothers others.