What is "crank preload" I'm in the middle of swapping my BB30 cranks from stock FSA Gossamer to a (shorter length) SRAM BB30 "IA" S950.  The S950 has a "crank preload" adjuster on the NDS which the spindle is also attached to.  The instructions are just some brief drawings, and I've had no luck finding good install instructions online.  One question I have is: 

What the heck is "crank preload".  

Thanks!
Crank preload is there to ensure that cranks are not over tightened so that they cause premature failure of the bearings. It allows the cranks to be "finger tightened" prior to the pinch bolts been done up to the right torque. It's a way of ensuring the spacing is correct on the crank axle.