For unique IDs in databases, you want them to have common prefixes such that they are kept in rough time order in the database's backend, otherwise your indexes

For unique IDs in databases, you want them to have common prefixes such that they are kept in rough time order in the database's backend, otherwise your indexes can end up huge and degrade performance (especially in MySQL, that's where we got bitten by it). That's where Type 1s are great, but of course this article shows a major downside.