If you have had snakes for a while, you can tell when they are in feeding mode and when they are in "whats going on" mode. If a snake is in feeding mode and you need to preform cage maintenance, wouldn't you rather do it safely without the risk of being bit. If a snake bites you, your reflex is to pull away and this can be dangerous for the snake. Spraying them with a bottle of water might startle them, but its not "inflicting fear" or anything. They usually forget it even happened after a minute or two.
I don't spray my snakes because they don't bite. They just ball up.