A client recently said there was no point in usability testing a site on desktop and tablet as the site looks the same. We disagree. A site may look the same on both devices, but users behave very differently when using a tablet. Recently we tested a site which includes a TV programme guide. Five days worth of programmes on seven channels were visible. But by clicking on the guide and dragging, you can see what will be on over the next month and can also see what has been on over the last zillion years (this was a media archive site). Faced with this guide on a desktop few of our testers realized they could drag and scroll the content. But put a tablet in their hands and they were swiping away merrily and accessing content they hadn't realised was there on the desktop version. So in this case, testing on a tablet highlighted issues with the desktop site.