They are not effective for the advertiser very rarely does a click thru translate to a purchase, but they help websites make money for each click thru. I dont know how much Sherdog and other popular forums make anymore but back when Adsens first came out websites were making big bucks in the early days of it, but things changed when Google bought youtube now its the youtubers making big bucks off the ads.
But its tough to make money now on a forum or blog due to chrome and mozilla having a built in ad blocker.
The only way to make money from these adsense ads now is through YouTube since adblock cannot block the ads in the video, those videos will play or the ad will pop up its why youtubers make a killing Adsense generates over 20 billion in revenue a year and many of these youtubers who just post reaction videos and other crap stuff are able to make a comfortable living, many of them make anywhere from 30 to 60k a year and the big channels make high six figures to millions a year from youtube.
A lot of companies are complaining of taking a loss from advertising and not getting many conversions.