Question

what is significance of roll off rate in case of filter

Answer 1

A single pole role of is 6 dB per octave or 20 dB per decade and can be approximated by Bode plots. For every additional pole the you just have to add the dB roll off rate in the approximate Bode plots. Also along with gain roll off there's an associated phase shift plots, these become important if your going to use feedback, in either case with today computers more accurate plots can be made but then again it depends on accuracy of components.