The heavy thatch layer actually helps to retain your soil moisture until you can get a good rain. That's one of the caveats of this technique….you have to at least have some thatch to improve your odds of success. If there's too little thatch, and little to no rain in the forecast, your new seedlings may dry out before they get going good. In that case, it's extra important to seed right before a guaranteed rain.
I think there can be a point of too much thatch. I'm sure Mega can elaborate on that. But so far, I haven't run into that problem, even after mowing down 8-foot-tall sorghum onto the seed.
