Have helped with flats, derailed chains, brakes, misadjusted derailleurs. Probably the best was I spotted an inexperienced rider in a group. His seat was set way too low so adjusted that. While the bike was stopped, noticed the quick release lever was sticking almost straight out. He thought it turned to tighten, as would a bolt. Explained how it worked, set it, and he went on his way. It was the front wheel, so may have saved him from having a nasty wreck. He had borrowed the bike-maybe the owner didn't know how a quick released worked either?