OTAs and training camp can only provide so many fresh looks. Even for rookies, playing against the same guys day in and day out allows you to pick up on cues that may not translate to a game situation. Quarterbacks and coordinators may tinker with the looks they throw out there, trying and assessing new things. All in all, it’s hard to get a true read on a team based on training camp practices alone.
That’s where joint practices come in. With so little live action for each unit in preseason games, joint practices allow teams to throw their players into unfamiliar looks and see how they fare in a true wild card situation.