Nearly impossible to clean off fungus spores. And besides, most fungi are already present due to being carried in the air on winds, or spores carried by means of grass seed.
Weeds--also a difficult problem. But their seeds are almost everywhere, too.
The groundskeeper will be very careful to never allow outside equipment on football and baseball fields. This is to prevent the introduction of Poa annua. Likewise on the top-shelf golf courses.
Southern lawns--I am not sure--probably best to blow off clippings and residue. You do not want to be accused of spreading Bermuda grass to fescue lawns.