Here's my reasoning: Fitt's Law (http://en.wikipedia.org/wiki/Fitts%27s_law) is a computer interface rule that the smaller a target (eg a button you want to press) the longer it takes to get there.
This is why edges and corners of the desktop are easy to reach: they have essentially "infinte" width.
This relates to dexpot preview because I have it laid out vertically and autohide it on the right of my screen. Usually I get there by jamming my mouse all the way to the the right, and sliding down the edge until I get to my desired desktop. However, I can't simply mouse click there to switch desktips, because I only end up clicking on the resizing border. I need to move back to the left a bit before I click. Eliminating the border would make this switch easier, by using Fitt's law.
I understand you're probably rolling your eyes
as this seems like a small point, but consider that most people rarely resize their Desktop preview, but are ALWAYS switching desktops. So it adds up! 
Let me know if you have any thoughts.
