Based on an admittedly simple test, it appears that it only stops the notification. For example, turn on power saver with the vibration feedback turn off. The home and back buttons no longer provide haptic feedback.
Now stop force stop the app. The haptic feed back is still off. Go to settings, Power, and the power saver still shows on, and the vibration feed back still shows turned off.
Now do the opposite. Turn the vibration feed back back on, force stop the program, and got to settings. Power saver still on, vibration feed back still not switched off. Home and back still provide feedback.
Why they didn't just give a toggle for showing the power saver notification is a mystery, but it appears that it can be disabled this way if it bothers you.