It's my belief that to be involved with a recovery program, one never stops working the steps.
There are others out there who feel one only needs to work through the steps once (or certain steps).
In my experience, I've never met or heard of anyone who has relapsed while actively working the steps with a sponsor. When I do hear of someone relapsing, I like to ask what step they were working on when the relapse ocurred. The answer is always the same. They weren't.
But to answer your question, the 12 steps are the foundation of recovery. They are a simple list of... oh what to call them... exercises? That are a suggested program of recovery.
It's not unlike a physical excercise program. You have a list of certain, specific excersies you do on a regular basis. When working with a sponsor, it's not unlike having a trainer working with you. As you continue with regular exercise, you get stronger. The 12 steps are like emotional/spiritual exercise.