Why do you need GMT and UTC?

Question

Working with date/time

Why do you need GMT and UTC time? There are also time zones.

Answer 1

So that you can say: "The dead will rise at 4 o'clock GMT" and it became clear to the whole world when this will happen according to local time, because everyone knows the deviation relative to Greenwich Mean Time, but not everyone knows about Mumbai or New York (time zones) .