By default, Mission Control will always show you parameters of your currently object selection. Sometimes you may not want this behaviour; eg when viewing/editing modifiers, materials, or texture-maps. The “Pin” button will prevent Mission Control from changing the current class when your object selection changes.
When used in combination with the “Selection Filter” you can quickly see which texturemaps, materials and modifiers are associated with your current selection.
Please click the gif to view full-size.