What does the Pin do on the Unified Placement Tool Property Panel?
When the Unified Placement Tool Property Panel is docked to an edge of the screen, you have the opportunity to pin the dialog to that edge. This can help save valuable screen real estate, leaving more screen space for placing multiple components.
When "pinned", the Unified Property Panel will collapse down to a tab on the edge of the screen
If a pinned dialog is closed by clicking the X in the upper-right corner, it will be restored collapsed when a placement command is again selected.
To un-pin the Unified Property Panel, just "hover" your cursor over the collapsed dialog, allowing it to fully display, and then click the pin again.