Training SB i thought trained Rebounding and Inside Defense as well. If you Train say ID for a few weeks, then rotate over for example:
Weeks Training
2-3 ID
2-3 SB
2-3 RB
2 IS
Repeat
This should develop a well rounded big man and without sacrificing on anything especially if your training a good young player and you train them up until their in their mid twenties. Of course still work in other attributes like JS, 1v1, Passing and such as you see fit but SB is something i think is just as worth training as any of the other skills and easy enough to train without actually sacrificing on anything.
My lower salary players like Lloyd Sprague tend to be key throughout each season because of their builds that include solid blocking thats paid off very well against much higher salaried players at the same position.
I think SB is also good for reducing the number of fouls per game by your players in that whether their good or not, players are going to attempt blocks either way. If they are good a SB, theyll more likely make an actual block rather then a shooting foul. People keep saying the salary is gonna jump up from training it but i think whatever the increase is its worth it overall