By pressing T with a puzzle loaded, you can choose to view only certain pieces, for example the pieces with a certain number of bumps (a certain jigsaw puzzle shape)
This can be useful at the beginning of a large puzzle, when you classify pieces.
Choose one of the options offered and notice how only the pieces with that feature are displayed and the others are hidden (in fact they are displayed very dimmed)
In order to have better control to that group of pieces, you can move them to some tray and from there you can organize them and, eventually, move them back to the main board. (Remember that you can move groups of pieces so the distribution you make in a tray can be then moved exactly to some zone in the main board)
* If a piece not hidden is connected to others these will be displayed regardless of their type.
* These options are not available with these shapes: Cubist, Mosaic, Patches and Steps.