I still have a lot of situations where we discuss things on a video call or something and someone needs to figure out the math. If I instead say, "1300 hours UTC," and everyone is using UTC, it's easy for someone to say, "no, that time doesn't work, how about 1800?" or whatever. If you're dealing w/ multiple time zones (e.g. at work I deal with three, each at least 5 hours apart from each other), having one standard time is a lot simpler (we use our local time, because we're the parent org).

If you're scheduling things asynchronously, it doesn't really matter. But a lot of schedules still happen in real-time, either on a call or in person.