There are various interpretations of rule 15.3 in golf. In general, the rule covers the ball or the ball marker that could be interfering with play. Should a player believe that a ball on the green could assist another player, they can mark the ball and pick it up from the ground. If the player playing the shot notices a ball that could obstruct their shot, they could request the ball be marked. This rule only applies to the green.
At the start of the 2020 season, golfing regulators USGA and R&A clarified their stance on the rule. The rule was then interpreted in a more conventional way that will protect the interests of all the players on the course.
While leaving the ball on the putting green is still something you can do, there is a rule that suggests that if a ball will interfere with the shot of another player or assist them in any way, both players should make sure that the ball is marked and removed. Should the rule not be enforced and other players are not present, a penalty of 2 shots will be added for both the players who used the backstopping method.
While backstopping might have been something that players could use to their advantage, its benefit of it has greatly disappeared. Nowadays, backstopping does not create as much controversy and with punishment for both players, you will see many players mark their ball. It is much better to mark the ball and lift it to be on the safer side.