Ways it is helpful: 1)Friction is what keeps the bike moving. If there was no friction between the tires and pavement then it would stay in the same spot.
2) Without friction you could not press the breaks to stop the bike. So if there was danger ahead, you wouldn't be able to stop yourself from crashing or running into it.
Ways it is harmful: 1) If you press the breaks too hard while moving, the friction will cause you to fly off the bike and skid across the ground, causing your skin to scrape off.
2)Friction can cause wear to parts of the bike.
