Comment by ibejoeb

If you're using it regularly, you can make it a derived column and index it in most RDBSs. Then it'll work with predicate push-down and you can do other fancy things like store it on alternative partitions to optimize block reads when you're not using it.

The other obvious benefit is that it is no different in semantics than any other column, so there's no advance knowledge necessary for other users vs using a function.