I brush hog my fields about every other year. I would do it every year but can't find the time to do it all. If I let it go three years, the briers, pine seedlings, and scrubby brush take over. I notice that whenever I mow a field there is a definite increase in game activity -- primarily deer and turkey. I think the mowing exposes the fresh growth and makes it easier to find.
And yes, my tractor grills are just covered with fluffy stuff from ripe goldenrod -- they come out looking like a sweater.