Partly, I suppose it's what I'm used to from the docks I'm looking to replace with LaunchBar Commander.  The practical aspect is that with a dock that is only large enough to contain the icons, your mouse is near the icon you want as soon as the dock unhides.  You can center or offset the dock to either side.  Also, if it behaves like most docks and only a mouse over/edge bump in the area actually occupied by the dock unhides it, there is less 'collision' between unhiding a dock and say minimizing a window.

I've been playing with LaunchBar Commander a little bit, but there is one thing I can't figure out.  As soon as I dock a bar, it expands in size to take up the entire edge of the screen it's docked against.  Is there any way to prevent that, so that it only uses the space it needs?  I didn't find anything in a forum search.