Here are some reasons to add microbes.
1. Flooding and/or standing water on a turf will choke off all the oxygen to the underlying soil and kill off all the fungi. Compost or compost tea will replenish the fungi species killed off and give them a head start as opposed to waiting for them to fly in on the feet of birds or grasshoppers.
2. The use of a fungicide on turf will kill off the target fungus as well as non-target fungi. Some of these non-targets are beneficials and are needed in the food chain for organic materials in the soil. Compost to the rescue again. Insecticide, herbicide, miticide, and even chemical fertilizers have similar effects to much different degrees.
3. When dad decides to build a tree house out of CCA lumber and does all his sawing in the middle of the yard, the sawdust will leave a bare spot there for, oh...going on about 5 years now. Year after year of compost treatments is just now starting to show results. Nothing grows there but the spot is getting smaller (at least in my own mind).
4. A fungus invades turf. The microbial balance is already out of whack. By adding corn meal, the balance can be returned.
5. You have a fire ant mound in your yard. Fire ants hate sugar for some or several unknown reasons. By pouring 3 ounces of molasses in a gallon of water on the mound, the ants leave in 24 hours. Every time? Apparently not, but it's well worth a try. Apparently the molasses stimulates a bacterial bloom that may taint their food, infect their food, or just maybe make them feel sticky

We don't know yet - at least I don't know yet. Keeping a slight sugar balance in an area seems to keep fire ants out. And the sugar ants don't seem to pay any attention.
Is organics really just another way for people to meddle with nature, rather than really understand nature? A healthy growing turf will break up hardpan (from developer/builder sins) and will begin to create its own topsoil within a few years.
Turf grass growing and maintenance is meddling with nature. Some of your clients want the meddling done with organic materials.