I have a system. Oh, first the answer to the question; I stop at three patches in one tube. My system is to always have a spare tube along on the ride, either a patched one or a new one. In my garage I have 2 nails in the wall. One is marked "Bad Tubes" and the other "Good Tubes." The system is that I occasionally spend time out there patching tubes and moving them to the "Good Tube" nail. In truth, the Good Tube nail is empty. There's a small stack of new tubes on the shelf nearby. When Performance has a sale, the Good Tube nail just waits a bit longer.