I've seen a lot of people mention adding vegtable oil or crisco to chocolate for dipping. Why would one do that? What is the purpose?

I only add oil when I am putting chocolate in my chocolate fountain so it will flow freely. I think it keeps the chocolate from setting up so fast. also depends on what kind of chocolate you use. Wilton candy melts, I just melt and use.

The oil thins out the chocolate. Some chocolates are thicker than others once they melt. I have that problem with milk chocolate but not with semi-sweet chocolate. You can also add cocoa butter or butter. Not a lot though, just a little.

with candy melts just dip and go, but with chocolat add a little Crisco or Veg. Oil. It makes it more smooth and gives it a nice glossy finish.