I think it's psychological. If you think putting some extender in your paint will do something more than a splash of water will do, then perhaps it will. I have experimented and found that Floetrol and XIM do the same thing water will do. But I am a pessimist and I think most companies are trying to scam me, so perhaps I never gave those extenders a chance. I did notice though that adding Floetrol to the paint caused an issue with coverage. I was using a yellowish color that barely covered in two coats and when I put the Floetrol in, it really needed a third coat, so I do wonder if all extenders affect coverage or just the cheap ones? When I used the Benjamin Moore Aura extender and the extender made by Aqua Finishing Solutions, I found those to perform a lot better, but perhaps since I was paying more, I had prepared my brain for a better experience and so therefore, I had one.