This tool is useful to represent the preservation of volume in animations. For example, a bouncing ball.
Using Squash and Stretch
Select the points to squash and stretch.
Click the Squash and Stretch tool on the Deform tab.
Choose an axis as the Primary Axis in the drop-down menu on the parameter editor.
Use the Strength and Rolloff parameters to control the amount of squashing and stretching.
You can change the Operation of the deformation in the drop-down menu on the operation controls toolbar or the parameter editor, since twist, bend, taper, linear taper, and squash and stretch all put down the same node.
For specific parameter node help see the Squash and Stretch help.