[nickporter]

They are very useful when you want to build modular web components, and for just overall maintainability of your stylesheets.

I wouldn't reject someone because they don't know what rem is though! I'd think of the question as a bonus I guess.

[DigitalSea]

Definitely. You'd be silly to asses the skills of a developer based on such a question. My point was more-so that companies should ask questions developers would know instead of asking questions most developers would probably Google the answers to.