I've been to a lot of what I suppose are called "black tie" affairs. This is because I'm a musician. In the three-plus years I've been wearing kilts I've put on black tie to attend the San Francisco Symphony twice, and it absolutely wasn't necessary. However, it was fun. Aside from that, the only place I've worn black tie is X Marks Burns Night dinners, where it's also not mandatory (just encouraged).

Honestly, why worry about it if you've never been to one and you're unlikely to ever get invited to one? Not that there's anything wrong with being curious and asking, just don't stress over it.