From Game Dev Academy: "Suppose you’re building a platformer game, where the hero can walk, jump and attack. The hero can jump while standing or walking, but he can’t attack while jumping or walking. Also, the player can not jumping again while it is in the air (no double jumping).
We can start implementing the hero code as below. Depending on your coding experience, you may have noticed that this code is troublesome. To know if the player is jumping (and therefore, keeping it from attacking), we have to save its state in a variable, which says if the hero is jumping or not. Now, suppose we want the player to be able to block attacks, but only when he is standing without walking, jumping or attacking. We would have to add another variable to keep track of that. In addition, suppose we want to change the hero animation when it is jumping, blocking or attacking. You may already have noticed that it will be extremely difficult to manage this code as we increase the size of our game."