GGU-3D-TRANSIENT: "Special 1" menu item
A message box provides information on this function after clicking on the menu item.

You can thus restrict the occurrence of boundary conditions This can be useful in order to avoid a negative pressure in the system.
For example, this can apply to the water side of an embankment if a potential is initially defined at the top of the embankment and then the water level lowered to the base.