Understanding Auto-Complete

When does the auto-complete button appear?

When every card in the tableau is face-up (with no face-down cards left), the remaining cards can all be logically cleared to the foundations. That's when the auto-complete button appears.

Pressing auto-complete automatically sends the cards from the stock, waste, and tableau to the foundations in order, finishing the game to victory. It's a convenience feature that saves repeated clicking.

It's meant to quickly wrap up a game that's essentially already won, and it has no effect on the outcome (a win).