Sometimes you need to cut your model because of it's size is too big for your printer's print surface or to get a puzzle. Rich Olson made a OpenSCAD library named PuzzleCut for that exact purpose. It lets you easily divide objects into 2 or 4 interlocking pieces for 3d printing or laser cutting.
This is extremely useful little too with only two small obstacles for end users: you need to know how to use OpenSCAD and number of pieces is limited to 2 or 4 (probably solvable with some digging in Google and upgrades in future versions).
There are some other solutions for cutting models, but this one is able to position the puzzle cuts anywhere on the X and Y axes, adjusts the kerf for a tighter or looser fit, and exports one piece at a time for 3D printers with a smaller build area.