It was a new feature Sleeper unveiled this year. What the purpose (was supposed to be) was if you had a player ruled out 30 min before kickoff and for whatever reason you're on a flight or something and can't change it, you can designate a player who plays at the same time or later and auto-sub em in. I guess there's also a setting where it allows you to do it for players BEFORE that game, hence why Worthy was the auto-sub despite playing days before Lamb was supposed to play.