A mistake could drastically reduce ones territory even when the game is "decided". Of course such mistakes don't happen if the players know what they are doing and are giving a bit of attention to the game. But that's not always the case.

However, i also think that it is very annoing to play out the end when the territories are enclosed. I will resign when i see i have lost and wish my opponent would do the same. But if they choose to fill the board then so be it.

And of course a game of chess can be won without the queen. With experienced players playing that is very unlikely and at top level it's next to impossible. But at general BrainKing level it happens all the time.