Advantages of using vinegar as a salt substitute for enhancing flavor?
The advantage would be cutting some sodium out of your diet.  If you are like many in the western part of the world, you probably get more than your daily allotment of sodium regularly.  By making sure to cut sodium where you can, you gain the health benefits of a well-balanced diet.

Since salt is a flavor enhancer, a low-sodium diet can often seem bland.  Many look for alternatives.  Vinegar brings out flavors in a different way and adds a significant flavor of its own.  I'd start small, using just a bit of vinegar.