In the first two seasons of VAR there were some very confusing offside decisions. The lines drawn to the defender and the attacker would be on top of each other.
There were many complaints that this was against the spirit of the offside law.
So from the start of the 2021-22 season all leagues added a tolerance level, or benefit of the doubt, of about 5cm to the old offside technology. It meant that if the two lines touched, the player would be given onside regardless of the on-field decision.
This was because of inaccuracies in the technology, like the correct moment the ball has been passed.
In effect a player could now be marginally offside on the technology, but onside when the tolerance level was applied.
At the time, referees' body Professional Game Match Officials Limited (PGMOL) estimated it could lead to an additional 20 goals a season.
The advent of semi-automated offside technology (SAOT) changed all that. Other leagues, including the top flights in Germany, Spain and Italy, have gone back to offside by the millimetre.
But when the Premier League introduced SAOT it wanted to continue with the tolerance level, to give some leeway to the attacker. That is because there are still questions about treating this new technology as flawless.
It is also why you will get situations like Wirtz, who appears to be just offside, but SAOT will give him the benefit of the doubt.