I suppose it further reduces the chance of a collision. If you're in a totally random space, there's always a chance someone will generate a collision if you wait long enough. But if you follow the timestamp and MAC address rules, then for a collision to happen it basically needs to be the same computer hitting the same number twice on the RNG within one second, which is less likely.

But, since that only holds true if people follow the rules, it's worth standardizing on either v1 or v4, and so it's good to be able to distinguish between the two for validation purposes.