Yes, yes they do work. That's why it's a billion dollar industry. It allows industries to micro-target specific ads for communities and speak to them directly. It gives you more ability to expand your brand to new customers, not less, as it allows to you to specifically target niche groups who previously had no interest in you. It's important to get a sense of the extreme level of refinement that firms have access to through data-driven marketing. Want to design a marketing campaign for dog-owning, outdoorsy lesbians? Subaru launched an ad campaign in the 90s using subtle coding in their wide-net ads. Now companies can do that much more effectively by directly targeting those communities.
As for the common complaint that you always see ads for products you already purchased, that's actually a very good time to make an impression. What are the odds that you are thinking about buying a new dishwasher at any given moment? Probably next to 0. You probably would completely ignore any dishwasher ad you saw. Now imagine you just replaced your dishwasher with a new one. You probably noticed that dishwasher ad now. You might have even clicked on it to see if you got a good deal on it. You probably care more right now about dishwasher specs than you ever have in your life up to this point. Maybe there's a better deal out there. This is the perfect time to send you more dishwasher ads.
As for the common complaint that you always see ads for products you already purchased, that's actually a very good time to make an impression. What are the odds that you are thinking about buying a new dishwasher at any given moment? Probably next to 0. You probably would completely ignore any dishwasher ad you saw. Now imagine you just replaced your dishwasher with a new one. You probably noticed that dishwasher ad now. You might have even clicked on it to see if you got a good deal on it. You probably care more right now about dishwasher specs than you ever have in your life up to this point. Maybe there's a better deal out there. This is the perfect time to send you more dishwasher ads.