What is the significance of impulse response in system analysis?

The impulse response h[n] (or h(t)) is the output of a system when the input is a unit impulse. For LTI systems, impulse response completely characterizes the system - output to any input is convolution with h. In frequency domain, Fourier transform of h gives frequency response H(f). From h, determine: Stability (absolutely summable for BIBO stability), Causality (h[n]=0 for n<0), System type (FIR has finite h, IIR has infinite h), and Filter characteristics. Measuring impulse response is a standard system identification technique.