When pressing
If you select the On press option as the Trigger, the behavior rule is only applied to the element when users press and hold the mouse button on it, and is reset when users release the mouse button or when they leaves the element.
If Action Type is set to Set data point property, the value of the data point property will be reset to the old value that was present before the user pressed the mouse button. This behavior can be used to implement push buttons, where the data point should be reset to its previous value after the user stops pressing the button.
Please also read the related information under When clicked.