What does "Default" setting in Privacy really mean?

[Suspiria1488303077 5]

It's the setting default but your privacy is as you marked it When I checked off another besides default and saved it. THe setting remained as I checked it.

[Suspiria1488303077 5]

It's the setting default but your privacy is as you marked it When I checked off another besides default and saved it. THe setting remained as I checked it.

[Ember Topaz 0]

OH this is where it is.

:smileymad: Comments aren't visable by default.  Don't like that much

But to clarify if the option was set to Use Default (all) and I set to Friends. It sticks with friends. If it was set to to Use Default (none) and I set it to just the None option it flips back to Use Default (none) What happens if something gets messed with on the back end and the default for email goes from none to all does everybody's email become visible to all?