When should the stopband frequency be placed after cuttoff frequency?

I dont understand what effect the stopband frequency has after the cuttoff frequency. I understand lets say the cuttoff is 1000 Hz. It starts rolling of there at about -20db/dec. Now the attenuation frequency is suppose to be set i would assume a decade higher, and have it roll of at -45db/dec ? I dont understand how this effects the signal. Whats the benefit of making it closer (if there is any) to the cutoff frequency? Also the drop of rate of -45db/dec , if its increased what does that do the signal ? Also whats the benefit of making something roll of faster at the cuttoff frequency fc ?

Sorry to say, but your question doesn't make much sense. The stop band is not the frequency at which a signal rolls off at -45db/dec. It's simple the band of frequencies that are "rejected" by a filter. What you're asking about is something else, but I'm not sure what it really is. Please specify what kind of circuit you're looking at, and maybe we can figure out what it is you want to know.