An absolute waste of money, time and effort. For all the good it is you may as well toss a coin . . heads it's offside, tails it isn't.
Can't believe people are suggesting changing the offside rule (again) just so it fits into the VAR framework
As mentioned though, if it's something clear and obvious that the officials missed I don't (can't) see a problem with it, trying to measure millimeter accuracy however, is simply guesswork