Not only are they useless, they cost me money as a customer. Every company paying for ads, needs to earn a greater margin to cover the cost of ads. If the entire ad market collapsed and products instead needed to compete on price, quality and overall value delivered to the customer, we would all be better off. Advertising allows firms to compete in a vector which provides me no benefits.
I would love it if we had a law that said once a product achieves more than something like 10% market share, it could no longer be advertised. Advertising for new unknown products makes sense. Once I know about a product, advertising just serves to divert resources from making the product better and to generate noise that dilutes the message from new products of which I might not be aware.
One of the biggest problems in this country and all countries are people who live their live accepting what they are told, instead of seeking out an answer to their questions and doubts on their own. People accept information from Fox, CNN, NY Times, NY Post, radio, advertisements, etc. at face value. Culturally, we would all be better off with an attitude like those who read and write the reviews for products on Amazon. I and every other customer get 1000x the value from Amazon reviews than I get from advertising. It has saved me from buying many many dud products and helped me discover the products that provide the best value. Plus, there is only so much any manufacturer can do to game those reviews since it is eventually self-correcting (i.e. pay for good reviews increases sales among the misled, who later show up and post most honest reviews that will be less favorable or downright negative)