point of silent mode?

Can somebody please help me out here... what's the point of silent mode?!

I would think the silent mode switch on the side of the phone would be universal, I.e. not allowing ANY sound to come from the phone at all. I frequently ride the train to work and hate it when I go into various apps and find that the volume is way up and blaring. I have to rush to turn down the volume, which gets annoying even after I've set the volume all the way down several times throughout the day.

If they've already set the ability to adjust notifications and sounds from each app we download onto our phone, then they should make silent mode universal like it used to be.