Imagine a distributed system where you want to preserve uniqueness across the board. Using a uuid more or less (by the sheer number of possibilities) guarantees that this will be the case.
UUID v1 uses the MAC address of the computer doing the generation as a part of the UUID, which ensures uniqueness so long as you aren't cloning MAC addresses in your infrastructure.
The downside of this is that it can leak information about the machine that generated the UUID, but if you require deterministic uniqueness, there you go.
The downside of this is that it can leak information about the machine that generated the UUID, but if you require deterministic uniqueness, there you go.