I would disagree, depending on your definition of "intelligent knowledge." I bought a Macbook a year ago with tons of software that I find really valuable. And since I've never had to restore my OS because Macs are so reliable, I've essentially been using over $1,000 worth of free software.
Sure, I wouldn't have paid the value of the software without the discs, but it definitely made me choose to buy that person's machine over an "empty" one.
To the OP, I can't tell you from a tech standpoint, but I've sold 4 computers in the past leaving the software on and wiping my personal info, clearing all cookies and histories, etc., and I've never had a problem.