someone else will probably be able to explain it more in depth than i can, but to my understanding the biggest thing is, without it blocked the friction disc is in constant contact with the flywheel, and that causes it to trap moisture in the form of condensation. the disc will be warm from use and then as it cools it will collect the moisture, especially right now when it's cold and damp outside. a layer of rust will form on the flywheel, and if left for very extended periods of time, can even lock to two together as the friction disc is "porous" and the rust will actually form into it. each time you use the tractor that rust has to wear off before you get a good amount of "grip," and if the pressure plate is worn or weak to begin with it makes it that much worse.
as for if it a stop-gap measure, i would say even if it is, if it helps, just do it until it no longer helps and fix whatever needs fixing. HTH, Matt J.