Why is resonance important in musical instruments?
Resonance is distinct from a source of sound in that it is naturally sustained without any input of energy.
A tuning fork resonates and thus produces sound with only a brief input of an impulse of force. The sound sustains until the damping [loss of energy per cycle] removes the energy. The damping is very small so we say the damping coefficient is low.
Musical instruments [string, brass, percussion & wind] produce sound by resonance too. Waves travel along a string, air column or cavity bouncing back and forth to produce a natural oscillation. Damping coefficients are usually modest depending on the instrument.