One you've switched from one to the other, chances are you have both installations running right up to the house, and switching back is literally a matter of swapping one cable connector.

If you have your own inside equipment, (Tivo, cable ready TV's, whatever...), so don't have to mess around with trading cable decoder boxes back and forth, there's little reason to not keep switching back and forth once a year and always get the introductory price offered to those customers just "stolen" from the other guy.