Why do we do spectral estimation

[SanjKrish]

Hi all,
There are various methods through which we estimate spectrum of a random signal like parametric and non parametric methods. But when I googled as for why we do spectrum estimation I don't get any answers.
Can anybody tell me some instances which you would have come across for which u needed to estimate the spectrum of your signal of interest.

What does it provide which time domain doesn't provide.

 

[axcdd]

It provides frequency components of random signal.
'Random signal' could be some sort of information signal covered in deep noise (or its just not white noise etc.), so time parametric method would miss it.