This is a feature that many other software packages that feature draggable tabs, palettes or bars has. For instance in most web browsers you can rmb and pin a tab, its possible in Visual Studio by clicking a pin.
What this helps with is accidentally dragging tabs out when you were simply trying to bring them to focus, I have had instances where dragging a tab accidentally has crashed the editor because it was attempting to snap it everywhere my cursor went. It sometimes even gets stuck in tab snap mode or other weird errors from an unintentional drag of a tab.
This feature would mean we can lock in our preferred layout and not have to work out getting in back when things go awry.