[jordanthoms]

This is dependent on the database you are using - if it's a key-sharded distributed database, you want to have insertions evenly spread across the key space in order to avoid having all the inserts go into a single shard (which could overload it)

[cogman10]

This is the great thing about using random bits for the lower bits. Because you are unlikely to use more than say 2^64 database nodes, any sharding algorithm will have to figure out how to spread a key with 64 bits (or however many bits are in your key) across n nodes.

Because of the random portion of the key, that means you'll get good distribution so long as the distribution algorithm isn't something stupid like relying solely on the highest order bits.