most that usually happens is a bit of dry cut grass is kicked up, which I don't worry about too much
Don't know a piston would fare, but would assume it could be sucked in and clog the filter. Squadron had it happen on a Huey hovering over fresh mown grass and found the problem when investigating the far higher than normal EGT. Hovering down the line of revetments when a full sheet of plywood attacked the rotor and left the Huey with an enormous vertical. Maintenance reckoned the mast was twisted.