SB is a very important skill for a PF and C,but they cost you a lot more salary.
If you play against a team where the guards has a lot of driving skill and inside shot its a very usefull skill if your big men has some SB ,because they can stop those kind of players with this skill.
But most managers don't train that skill a lot and train more passing on those big men,mainly for there salary,so thats a choice you have to make,but SB is a very good thing to have in your defence..