I love when I'm checking a website on my phone and it redirects me to the "mobile optimized site" which is apparently an ad, or worse, video-ad, that takes up my whole screen and repositions when I scroll so that I can't close it and have no choice but to watch the ad. Then it's over and doesn't disappear properly and the content is left blocked and inaccessible. If I'm lucky the ad goes away and the site's helpful mobile-friendly navigation menu with dropdowns and popovers expands over the content I'm trying to read, obscuring it, or causes everything to constantly reposition itself. Then every time I scroll down to read further a new ad pops up at the bottom of the screen. This tells me you don't care about your content and you don't care if people read it. I'll spend my time elsewhere by closing the browser tab, turning off my phone and trying to remember to never bother with that site again.