Here is the post I found about this: It's in shopbot accesories titled "Indexer with a larger than 6" diameter". The following statement was in there made by Gene Marshall---- "A Good Tip...
turn off the control box and unplug the indexer before mounting the blank. "If you happen to turn that head chuck while it is connected, you will be shipping a control board to durham NC before you can say OH $#!T.
I wouldn't know if that pertains to both standards and alphas, or like I said, if it's an actual fact/myth.
The post I listed above also talks about some heavier items that are turned.