GroupAddUnitSimple() Vs. GroupAddUnit()

Anybody know the difference between these functions, like

GroupAddUnitSimple()
GroupAddUnit()

GroupRemoveUnitSimple()
GroupRemoveUnit()

ForceAddPlayerSimple()
ForceRemovePlayer()

What does "simple" mean in this instance? I do notice that their parameters are flipped around. Is this the only difference?

Yes, basically the requirements are just switched around. Don't ask me why blizzard did this because I have no idea.

They only have a purpose for GUI as the order in which the parameters appear in the text need to be the same as the function that the code generated from that calls.
In JASS they are completely useless and you should rather use the natives directly.

Which is why GUI can never be as fast as JASS.