Walk on your lawn. Does it feel like a mushy trampoline? That’s a bad sign. Pull up a small tuft of grass; if you see a thick layer of brown, matted crud beneath the green, that’s your thatch. Also, if moss has declared your yard its permanent home, scarifying is the eviction notice. Moss loves a soggy, compacted, thatch-filled lawn. Scarifying starts the eviction process.
Another giveaway: water repels off the surface instead of soaking in. You spray your sprinklers, and the water just runs off into the driveway. That’s your lawn saying, “Bro, I’m waterlogged under all this junk.” Listen to it.