A JB is necessary for multiple reasons if you're aware of the abundant flaws and shortcomings in the software,
But for sounds it enables you to download an infinite number of third party sounds
Seriously, man. You do not need to JB to add sounds. You need iTunes.
I use 3 different ringtones for calls, and various sounds for the other notifications. All 3 ringtones I created (adjusting existing audio to what I want) and installed, all before I JBed the phone.
My phone sounds are generally on, except in meetings or other places it must be quiet. In those places, sometimes I use vibrate, but I often don't hear/feel the vibrate, so it isn't very useful to me. I use the phone as my alarm clock, so sounds are on for night, too. And I would want to get any calls in the middle of the night, they would be emergencies, so definitely on.