When working with diagrams, you will often encounter the possibility that several shapes belong together as a group and that you would like to work on these shapes like they were one complex shape. This is possible with OmniGraffle; you can group shapes together to become a single shape.
If you have used corresponding group functionality from other software titles, you may have become annoyed that you must ungroup your shape groups—change one shape—and then regroup your shapes again. With OmniGraffle you do not need to be annoyed anymore. In fact, you can change just one shape in a group of shapes. This is pretty cool and a great time saver.
You can also apply style formatting like color fill, thickness of strokes, font formatting, and so on to the whole group. When you do this, every shape in the group will inherit this new style.