It can't hurt knowing the theory of bike repair. There are a number of things that I do myself: repair flats, change tires, repack bearings, true wheels, adjust brakes, replace brake pads, change chains, change rear clusters, change pedals, put on seats, put on computers, adjust deraillers and some other stuff. Some things I don't fool with because I only need to do them once in a blue moon or never. So why have the tools? Also, I don't do handlebar tape. I can do it but I never get it looking as nice as the bike shop does.