You just made TWO typos: "display-name" vs "display_name" and "_name" vs "name", automatically counter-argumenting your point.
It is also for documentation. With the declared constants, we know all possible values. With plain strings, how am I supposed to know which values to use?
It is also for documentation. With the declared constants, we know all possible values. With plain strings, how am I supposed to know which values to use?
The benefits far outweigh the marginal cost.