The Power Good signals are not intended to be used to switch ON/OFF the power rail.
A soft start such as indicated in figures 2-25 and 2-26 is actually better for nicely starting up the attached devices.
As ivan747 said, the Power Good signal can drive reset inputs to allow the circuits to reliably start at the correct state when the power is stable.
Another use is for chaining the start-up of multiple regulators (i.e Power Good of the first regulator to an Enable/Shutdown of the following one) in order to ensure the correct sequence of the power domains for devices (FPGAs, MCUs, CPUs, etc) that are sensitive to this aspect.
Cheers,
Dan