If freezing weather ever arrives this year, any mud, dirt or other abrasive, foreign crud frozen to the bark of any wood you're cutting is going to act like concrete or granite boulders on your chain. You will be truly impressed with how quickly your chain becomes virtually useless under these conditions. At that point, the question becomes whether or not to keep cutting to try to get through this tank before tackling the tedious job of restoring the edge to your cutters. You might say, "well, hell--the chain is already dull, so what harm is another ten minutes worth of cutting going to do to it? The answer is: plenty. Aside from the fact that cutting with a dull chain puts extra strain on the saw's bar, the sprockets, vibration dampening, your arms, etc., cutting with an already-dull chain puts a tremendous amount of extra wear and tear on the chain. That's because as the angle of attack becomes blunted, the blunt area begins to grow at an alarming rate as it hits the wood, which is, after all, an abrasive. Remember that your saw is running at around 15,000 rpm, which means the chain is really moving. And of course, an extra-dull chain takes much longer to restore than one that is simply dull or--better yet--one that's still sharp. And even if you are able to get it sharp again, the rakers will be so far out of whack that it may never cut again. Whether you've hit something or simply feel the chain starting to lose its edge, always stop immediately and sharpen the saw. By putting off the inevitable you not only make it more difficult for yourself, but you actually make things a lot worse in a short amount of time. In short, you have nothing to gain--but much to lose--by running a dull chain. At minimum, you should be filing your chain after every tank--and more often than that if it needs it.