# Why make the phase of an FIR filter linear?

I am new to DSP and filter design. It is easy to design an FIR filter with linear phase by making the coefficient sequence symmetric. However, why make the phase linear?

Because linear phase of a filter results in constant group delay according to the relation between group delay $\tau$ and phase response $\phi(\omega)$ of the filter: $$\tau = - \frac{ d\phi(\omega) }{ d\omega}$$