# Why band-limit a signal?

A Band-limited signal is defined as a signal whose Fourier Transform is zero above a specified frequency. Shannon Sampling Theorem is also stated for a strictly band-limited functions,i.e,

"For a band-limited case, 2W numbers per second are sufficient."

Where, "W" is the max. frequency content.

My confusion is that why band-limit a signal? What would be the situation if a signal is not perfectly band-limited?

My understanding says that unless we have a band-limited signal, we can't get a usable "W" and aliasing would also occur. Does it make sense as an answer?

I think I know answers intuitively, but struggling to frame it in words. Please guide me.