This came up a couple months ago where it was suggested we turn off HP ads if we have a lot of ad capsules (Amazon, Ebay) that are doing well, to decrease the distraction for readers. It really depends on if your hub is selling a product well and bringing in significant earnings. If not, it's best to keep the HP ads on because you're guaranteed something instead of nothing, based on pageviews and, I believe clicks, even if they don't buy.
I tried the "experiment" with some of my hubs and it was not good. Earnings went way down. So I turned them all back on. I have very few products on very few hubs (books, seasonings for food) which rarely sell, if at all. It was suggested we remove those ad capsules if we're not making any sales and stick to the HP ads.