I'm new to the iPhone world, although I've been down iPod lane for a few years. One thing that is well-known (and even parodied) about Apple devices is the slimmed down and minimalist approach.
So it strikes me as odd that there's a dedicated switch on the side, just for silent mode. There's already the control center for many similar 'quick go to' things, which also includes 'do not disturb' (which in turn doesn't seem that different to me).
So what's up with the one-function switch on the side?