I would respectfully disagree on the teflon tape not being a sealant.If you wrap typical pipe plug,it will even usually seal when just snug,as the tape is more like a ribbon packing of teflon.
Thats why in a pinch it makes good valve stem packing,just like graphite ribbon tape etc.,and why a leaking ferrule,even new say 3/8 plumbing ferrules will stop leaking with a couple wraps and require less tighnening.No lubrication is involved,just a layer of packing material around the ferrule,to crush on the seat.
tom