In laser locking, e.g. using the PDH technique, the light (say of frequency $f$) is modulated so as to add two symmetric sidebands of frequency $\Omega$.
I know the maths, I understand how this leads to the error signal etc.
Physically and intuitevely, how would I choose the modulation frequency $\Omega$?
I.e. : it should not be the same as the carrier light because... / it should be far or close to it because...