Setting the delay for slightly longer then the actual distance gives the effect that the sound is coming from the main stage area rather then the delays.
Ah, the Haas Precedence Effect. I've found that using additional delay (beyond what is needed for a phase alignment) doesn't provide enough benefit to justify the messing with the alignment.
The advantage here is main volume can be lower, speaker are not aimed at walls, reverb is less, feedback issues from mains is less.
The disadvantage is if the talent walks into the delay field he hears the delay which may disconcert him/her and make it difficult to sing on pitch.
I don't think it would be any worse than simply being X distance from the mains. Even if there was no delay ring/zone/fills, a performer or presenter that far from the main PA would still be subject to the same speed of sound, time-of-flight. Acoustic or electronic, it's still distance=time.