With xfce4-panel 4.6 I was able to place it at top/bottom of desktop and still keep it floating. See the screenshot and you'll known why I need this: it's an essential part of my desktop layout, and why I turned to xfce4-panel in favor of gnome-panel. I have title bar buttons on the left side, and made the panel overlaps the right part of title bar (where nothing is present) to save screen space.

However with 4.8, I can no longer specify the panel to be floating or docking; it automatically docks when I place it at top/bottom, and floats when I pull it off the edge of desktop.

By editing the configuration file, I was still able to achieve this:

<property name="position" type="string" value="p=1;x=1000;y=0"/>

However, this is not very convenient, as each time I try to move the panel the default behavior of 4.8 gets restored.

This could be considered a regression. I hope to see the old behavior of 4.6 restored (no automatic docking/floating), or (even better) we could add have an option like (parenthesis donate radio button):

 docking / floating mode:
 ( ) let xfce4-panel choose automatically
 ( ) let me specify
     ( ) docking
     ( ) floating