it always/never pays to do something
it (always) pays to (do something)
It is (always) a wise or advantageous idea to do the thing specified; doing this specific thing will (always) yield a positive effect. You can have the best product in the world, but if no one knows about it, no one is going to buy it—that's why it always pays to advertise! In my experience, it pays to have a seasoned legal expert look over every deal you're making before you sign the paperwork.
See also: pay
it never pays to (do something)
It is never a wise or advantageous idea to do the thing specified; doing this specific thing will never yield a positive effect. While it may be tempting, it never pays in the end to exaggerate the list of accomplishments on your résumé: if you don't get caught during the interview, you'll be in a heap of trouble once you actually start the job. In my experience, it never pays to try and make short-term earnings by avoiding paying your taxes in full.