My rationale is that, if Zoe gets in touch with me saying there's a job at Yves' company she's interested in, and could I introduce her? I want to be able to honestly tell Yves either that I know Zoe's work first hand, and she's excellent, or that I know her work's reputation, and it's excellent.
This means I decline (or simply don't respond to) around 20% of the invitations I receive. But I keep hearing that the point of LinkedIn is to expand your network as much as possible. Am I being too conservative?