It depends on what your front speakers are capable of, and what setup capabilities your receiver has.
If they have frequency response down to 50 hz, for example, you don't want an excessive overlap between the front speakers and sub, so the sub should be set to cut off above 60 Hz or so.
On the other hand, if you have tiny front speakers that only go down to 100 Hz, then the subwoofer needs to operate up to that frequency.
Some receivers allow you to set the rolloff individually for each speaker and some will set them all the same, so it depends on the functionality of the receiver setup menu.