In Power user you can decide if you want to se properties and viewer at the same time. This is not possible in Power web and is a problem for me. In power web it takes several clicks for me to see the documents "View Rendition". In Power user only have to click on the document once to see both properties and viewer. If you are looking at several 100 ever 1000 of documents in one go the additional clicks are a problem.
From my point of view , it is possible to have both properties and viewer opened at the same time in Power WEB. You need to first detach the viewer, you can do that in the top right icon in the viewer ( see attachment). If you have 2 monitors, it works fine, if you have only one, then it may be little bit strange if you have other windows and browsers openeded in your desktop.