Where is a version 2 UUID used?
In DCE systems — the distributed computing environment whose specification the version comes from. Outside it version 2 is hardly ever seen: many libraries can parse such identifiers but not create them. If you do not need DCE compatibility, pick version 4 or 7.
Why does version 2 store time so coarsely?
Because the lower 32 bits of the timestamp are replaced by a local identifier. What remains gives a step of roughly 7 minutes and 10 seconds, and within such an interval uniqueness rests on the clock sequence and the node address.
What does the domain field mean in a version 2 UUID?
It says what the number inside stands for: 0 is a user, 1 is a group, 2 is a value whose meaning the system defines itself. Here the domain is always 2 and the number is taken from the current time, so it points to neither a user nor a group.