This application allows you to capture the entire screen, the active window or a selected region. You can set the delay that elapses before the screenshot is taken and the action that will be done with the screenshot: save it to a PNG file, copy it to the clipboard, open it using another application, or host it on ZimageZ, a free online image hosting service.Thats what the developer site is writing about this tool.
On my point of view, it is easy to use, has a small memory footprint and works quite well. If you have another tool that is better or has other advantages, throw it in as a comment :-). While you are using something like "fbrun", a softlink in your "/usr/bin" as "ln -s xfce4-screenshoot screenshoot" should speed up your daily business (so you have to tip "screen" and hit the "tab"-button).