One of the key-features of PowerResizer is window-docking: with PowerResizer you can organize your window in an intelligent way. Try the following: run PowerResizer, then dock a window in the left-half of your screen (simply dragging-it with your mouse to the left of your screen) and another window in the right-half; now you can resize them using either the left border of the right window or the right border of the left window... the magic happens!

So, if you want either compare some documents or rapidly resize and move your windows, PowerResizer allows you to do some actions (such as resizing a window mantaining its center point fixed) by using some keyboard shortcuts during moving or resizing that window (see Readme file included in setup package or sources).