I use Kickin Walleye especially in Cold water. I am not sure how much it helps but convinced it doesn't hurt. Many times over the years I have had walleye take the first cast after applying this scent. This stuff really sticks to plastics as I can still smell it a couple of hours after applying it. If I can smell it I'm sure the fish can.
One day fishing the Mississippi and catching lots of walleye and sauger below Genoa dam my brother and I were neck and neck with about 20 apiece when fishing slowed. Then he rallied and caught the next eight. He admitted he started using the scent. We had on the exact same jig and plastic colors so the only difference was the scent. I have also had days when plastics that come with Anise scent seemed to out produce the same color unscented.
West coast salmon fishermen are much more vigilant about scent. Some scrub their hands with toothpaste and others wear rubber gloves before handling baits. They wrap herring strips on hard baits, use hollow cavity baits filled with tuna and garlic and many smear various Pro Cure scents on their lures. I use a lot of Brad's cut plugs with garlic roasted tuna in oil and convinced it helps when fishing is slow.
I read an interesting article about a study done by Jason Halfen using Trigger X. He demonstrated that fish held onto scented plastics longer than unscented. I'm sure there's a chance he has a bias but I think there is a lot more to be learned about using scents for fishing.