Imagine authority is money, and a particular page has $10 in “authority” to spend. It links out to 10 pages, so each of those pages gets $1 ($10 divided by 10). If it links to 20 pages, each gets 50 cents ($10 divided by 20). If it links to 5 pages, each page gets $2 (you get the math by now).
So rather than being able to apportion a page’s link juice, now you can only choose whether or not to pass that link juice on—the link juice you don’t use evaporates. Danny extends his monetary analogy to explain:
Again — and being really simplistic here — if you have $10 in authority to spend on those ten links, and you block 5 of them, the other 5 aren’t going to get $2 each. They’re still getting $1. It’s just that the other $5 you thought you were saving is now going to waste.
As Danny also points out, this doesn’t mean you have to run out and take off all the PageRank sculpting you’ve done—it just means that the link juice isn’t as strong to the un-nofollowed links as it used to be. If your site is performing well, the nofollows aren’t going to hurt it.
What do you think—are you going to run out and make changes to your sites? Did you see a marked improvement from PageRank sculpting (or not), and have you seen a change in that recently?