Years ago, I attended a salmon fishing seminar at the Vancouver Boat show. When the question of using scents on lures came up, the speaker referenced an experiment using scent versus no scent on lures with salmon in a tank. While the scent did not "attract" fish, they found that depending on who had handled the lure, human scent often times repelled the fish. Apparently, some of us emit a strong odor (especially after several days fishing I suppose) that will actually repel the fish. So, really what you are trying to do is mask your scent. Which is why some people use WD-40 and apparently it works too.
Given all of the other things that most fisherman will spend money on to improve our odds of hooking up, adding scent is probably the least expensive one. Kind of like a teenage boy using aftershave I suppose - it may not improve their odds, but they certainly think it does.