We use MDC at work. Usually the MDC bursts are filtered by the PL tone, so end users don't often hear it. Scanner listeners that run carrier squelch will.
On the ham bands, many run carrier squelch and will hear it. Most don't know what it is, and that tends to piss off amateurs. They'll usually complain (and loudly). That can be a good reason to run it, or not.
Some have set up their repeaters to require it. That's a handy tool to have to keep most prying users from accessing repeaters you don't want them to.
If you have to listen to it a lot, it gets annoying. It's a cool thing to play with, and figure out how it works. Good knowledge to have. But, yeah, it's got it's place, and FRS/GMRS/MURS/amateur usually isn't it.