Maintaining Tire Pressure: Tires naturally lose air over time (clincher tires lose about 1 PSI daily). Using a pump keeps them at the manufacturer's recommended PSI or Bar, which lowers rolling resistance, improves pedaling efficiency, and ensures a smoother ride.
Repairing Flat Tires: When you fix a puncture or replace an inner tube on the road or at home, a pump is required to inflate the new or patched tube.
Preventing Damage: Proper inflation prevents "pinch flats" (snakebite punctures from hitting curbs) and protects the bike rims from bottoming out against the ground