The bench can be somehow helpful if there are reserved that are future superstars. But most of them are just literally for reserve and we've only seen a few of them that came from being benched to becoming a first five. And for these games that are in the finals, the team has to secure their title especially for the Boston and they'll only be given playing time if the time is lesser and the lead that they have is no longer reachable. We get to see this kind of plays from teams and allowing the benchies to play and have some play time but it doesn't really matter that much at all.

Or, when their opposing team is on the lead and they can't reach it anymore. And so, coaches allows these benchies to play and just let the time tick until it goes to zero. Let's see if the Celtics are going to do that but IMO, Joe won't allow that and they have to secure this and everyone from the bench is going to understand that. Or who knows if they'll be given playing time this time since it's very likely that this is the last match of the series.