In scrimmages, when I have a guy who needs to play the whole 48 mins, I "let them play".
For big time games, it depends. If I'm playing a better team and absolutely need my best guys out there to level the field, then it may be worth risking "let them play". It also depends on your players, if they are prone to fouling or not. If your team doesn't commit many fouls then it's a smaller risk letting them stay out there