It's not an inherent advantage, but it can put you in advantageous situations against certain sparrers. The main thing is that is weakens sparrers who rely on fast reaction time, offensive moves, comboing, etc. It moves the dial in a spar from it being a test of who's better with mechanics and capitalizing on mistakes to a test of who's better at predicting their opponent.

I don't think it's much of an advantage, but a lot of people allow it to seem like it is because they either don't enjoy sparring against delayers or they aren't good at it… There's a way to spar them, so proving "delay is an advantage" by saying you're good against non-delayers but bad against delayers doesn't prove anything, it just shows that you're bad with being patient, prediction, etc.