This is a large button that appears in the bottom right of many of Google's Android apps. The button floats over the top of the content.
To me, I think this looks visually bad and it blocks the view of content. I am used to buttons residing in a bar of buttons, not floating above content. Another drawback is that there can only be one floating button, so only the single most common action can be placed there.
On the other hand, this type of button does provide extra screen space by not blocking content with a bottom bar. It also allows frequently pressed buttons to be placed near the bottom of the screen, closer to the user's fingers on larger devices.
Does this type of button provide a good experience for the user? Should it be used in other apps? Or was this just a bad design decision on the part of Google? Should this kind of practice also be extended to desktop and web applications? Please provide reasoning and even better, studies or articles to support your answer.