For preseason if you follow the NFL's model of:
game 1 - rest starters after 1st quarter
game 2 - rest starters after 2nd quarter
game 3 - rest starters after 3rd quarter
game 4 - rest starters after 1st quarter
you give your starters the chance to build their conditioning (which is low at the start of the season and the reason they get injured more frequently) without too much risk.
Also, don't think of 'probable' as an injury as much as just knowing they are a little banged up. Players are marked probable more frequently here than in the NFL because in the NFL the coaches are aware of very minor injuries that don't make it to the injury report, but here there's not really a good way to get you that information without requiring you to look at each player's health each week, so 'probable' isn't necessarily an injury that you should reduce playing time for.