Sometimes when you're interviewing someone, you want to draw their attention to a certain part of the code. In the past, you could do this by telling them which line number to look at, which works, but is kind of a pain. Now you can just highlight the text and they will be able to see what you're highlighting.
Anything text that you select will be highlighted in yellow on the candidate's screen, and anything they select will be highlighted on yours.
This should make it easier to communicate as you're working through interview questions with candidates.