This is a classic case of "I try stuff so you don't have to". I was very curious about Lip Lock from Face Atelier, a product meant to make your lipstick last longer. Basically it's a shellac. A clear liquid that forms a top coat over the lipstick to lock it into place. A great idea in theory that is probably useful in special circumstances such as a red carpet appearance when you want to make sure that despite all the air kisses and whatnot your lipstick is still ready for a closeup.
Civilians, however, will find that Lip Lock is a bitter liquid that saps the moisture out of the lips and feels like what I imagine a coat of paint thinner or other hardware store product would be on the lips. It irritated my lips for about ten minutes every time I tried this Face Atelier product and generally felt unpleasant. Lip Lock does prevent color transfer to cups and utensils, but I've found that the drying effect can cause some feathering, depending on the lipstick formula. Some lipsticks also get a dull finish as a result of shellacking them with Lip Lock. I'd say that thick and flat formulas suffer less from this top coat, but my lips protested every time I used Lip Lock.
Bottom Line: You don't have to.
Face Atelier- Lip Lock ($22) is available from faceatelier.com (it's under "Effects", not with the other lip makeup products, which is also telling).