Whitechip: It's useless to people who don't know how to play the game.
I don't know how to play, and I find it very useful. ;-P
Seriously, I only figured out how to make it take effect on second play Act II. So, this post is really just a bump to help out other slow learners.
(I know I am dense, but I reviewed documentation and journal. I don't see anything that explains it takes more than a tap to grab hold. I thought it just failed an awful lot without the right stats. Would be my only complaint about manual and journal so far, really. Everything else is really well documented through manual, lore or Dandilion's story.)