Black has 32 points and White has 27+6.5=33.5 points (I assume no stones have been captured), so if both players pass now, White will win by 1.5. So Black wants to do something.
Case 1: White thinks it’s not necessay to respond to this move because Black’s stone can’t live, so White passes. Black agrees that this invasion is useless so Black passes. Since White got a prisoner, White’s score is 34.5 and White wins by 2.5.
After that, Black sees no solution so Black passes, White passes. White got one prisoner (Black 1) but one less point of territory (White 2), so White’s score is 33.5 and White wins by 1.5.
Basically it depends of your opponent answer. A move in your territory will be a point less if:
Your opponent pass
Your opponent didn’t just play himself in you territory giving you a prisoner more, which balance your own loss
Your opponent has still a dame or even a valuable move to play.
That’s only under territories rules (like the Japanese). Under area rules you simple have to maximize your area, and you lose points not because you put a stone in your territory but because you had a better move that your opponent will play himself. (consequently almost the same as territory rules if players understand how a game is processing from largest to smallest move).
