I've come across this several times before and I've never been totally clear on it either.

I think the idea is that if you're going to work in a particular state then you're presumably eventually going to become a resident of that state, and technically (legally?) your licence should match the state you're residing in.

Obviously if you have a licence from any state in the US then you can legally drive in any state.

I've only ever seen it in job descriptions. Nobody has actually asked me in an interview or brought it up once I've been employed.

Unless someone knows more than I do and tells me I'm wrong, I would think you're pretty safe to ignore it.