Never heard of delaying the drum mics. Once, I delayed the house speakers to "line up" to the sound of the acoustic drums coming off the stage.
It "sort of" worked. There were places in the room that didn't "line up"!
Your milage may vary.
I guess it mainly depends on how many delays you have. On some early digital console, you could only delay outputs (busses). So you could only delay the FoH. A good strategy was to line it up with the loudest instrument on stage, often the kick drum. On newer consoles you often have input delays, so you can line up every single channel with its real location on stage. The drawback is this delay will also be present in all the auxes, which will be a real problem if it reaches 20-30ms (20-30ft) and foldback are done from the FoH console.
On the other hand, delaying channels to match the real location (or, more technically, so that acoustic and reinforced waves phase do match) is more important in small venues, where acoustic sound is a great part of overall sound. So the places where you want delay are also the places where you need short delay.
What I do:
- I put some delay on the FoH bus to line it up with instruments at stage front. This delay will not affect any aux so no problem with foldback.
- I put additional delay on loud instrument that are located upstage, but no more than 10ms. This allows to compensate for 10ft from stage front instruments - a reasonable distance for small venues. I put the delay according to a "visual" estimation of the distance.
- I put no delay on instruments that have almost no direct contribution to the overall sound (folk Guitars, vocals, keyboards...)
Keep in mind that the ideal delay varies depending on where you find yourself in the house. Also keep in mind that digital consoles and speaker processors add a short delay anyway.
My small experience tells me that the benefit of input delays mainly concerns instruments with strong low end (kick, bass amp or double bass). The phase reverse switch can be very useful too.
I guess there could be benefit to set delays according to mic distance from each other, as for snare top and bottom, instead of FoH, but I did not tried this untill now.