I think it's to let you know that something else happens after the effect ends.
For example, if you're stunned by a dragon's frightful presence, after you are no longer stunned (at the end of the dragon's next turn), you take a -2 penalty to attack rolls (save ends).
In theory, you could have a ability that goes: target is restrained (save ends). Aftereffect: target is immobilized (save ends). Aftereffect: target is slowed. This effect requires three successful saves to get rid of completely.