Scents (paste and oils) serve two purposes: (1) to mask the human scent (L-lysine from the hands) and (2) provide a scent trail for "hard" baits, e.g., hootchys and spoons. The paste last longer when applied on hard baits than oils. I know a lot of folks that add scent to their cut plugs for an added scent trail. I very rarely use bait, so I have no idea how much more magical adding scent to a "natural" smelling herring can be (??). Seems to me that by adding scent, you'd decrease the effectiveness of the natural bait. Again, I am not a bait guy.... I can tell you that you'll be hard pressed to inject Smelling Jelly paste in a cut plug. Used a liquid like Pro Cure.