Set belt tension by numbers, not by feel. Get the force for a tension gauge, the frequency for a sonic meter, and the load your bearings will carry.
Tight enough to carry the load without slipping at start-up, and no tighter. The usual check is a deflection of 1/64 of the span (16 mm per metre) at the force from the calculator; new belts are set about 1.3× higher and re-checked after 4–24 hours.
Over-tension overloads motor and machine bearings, can bend or fatigue shafts and stretches belts. Repeated bearing failures on a belt drive usually point to over-tension.