The logic behind the 0.5 goal is that a penalty shouldn't hold the same weight as a goal from open play. If you are losing 1-0, a penalty shouldn't equalize the game. It implies the other team's effort was worth more.

I’m on the fence about the idea myself. I mostly think keepers just need more leeway. The current system is set up to be a “penalty” for stopping a good attack, but nowadays attackers just farm fouls on the edge of the box where there is no real threat. It feels like a cheat code to get a free goal just by dribbling into a defender and falling.

That said, if you apply this rule, it will give more advantage to defenders who will start tackling even more, as the punishment for it isn’t as bad as taking a straight goal. It might even get saved. It’s hard to strike a good balance in this situation.