What about the players on a pitch though, they react to the linesman's decision in real time. So Oliver just listens to his headset, turns around and says :"Sorry guys, I've just got word from my VAR man, my linesman was wrong, so now it's a penalty instead of an offside." They've just opened a Pandora's box that will lead to more problems than solutions. How many situations like last night's are about to take place? It's been hours and people are still debating whether Kane was onside or off. Technology is a great help when it comes to checking whether the ball crossed the goal line but perhaps some things should be left well alone, even if it means referees/linesmen will keep making mistakes on occasion in real time.
This is not to bitch about last night's result, what's done is done. I'm just saying technology isn't always the answer.