I have learned what pot likker is from reading various Southern novels: the juices left in the pot from cooking vegetables and meat. Sick people were told to drink the pot liquor and no duh, because the cooking had leached all the good stuff into the water.
So after I steamed vegetables, I started straining the pot likker into freezer boxes instead of the sink (true confession: I don't always let it cool down - so maybe I have canceled the good by putting hot liquid into plastic!). Now I have a stash of free vitamin and mineral laden liquid to use in soups and the like.
If I think the flavor will be too thin, I do add a little powdered bouillion or salt. Sometimes I'll use part homemade stock and part pot likker because making stock is a long process, whereas collecting pot likker is not.
It's thrifty in several ways:
1. saves money because I don't have to buy vegetable stock
2. preserves health because there are valuable nutrients in the water
3. saves time because I'm already cooking the vegetables and the pot likker is an incidental product; I don't have to make or shop for vegetable stock