[adrianmonk]

It depends on what scenario you're talking about. One scenario where delay is often used is when you have speakers at different locations to provide even coverage for a crowd.

For example, at a really large outdoor concert, you might have speakers near the stage, and another set of speakers further back. If you don't add any delay, then the people sitting far back will hear the signal once from the speakers closest to them, and then they will hear it again from the speakers that are further away (by the stage). The effect will sound like an echo.

So you delay the sound coming out of the further back speakers just enough so that as sound arrives from the stage, the speakers further back produce it at the same time.

And it's not just large venues. in small venues, you sometimes cannot cover the whole area evenly with one set of speakers, so you might have small "fill" speakers to deal with coverage gaps.