I have already run into this at work. I have customers whose keys are publicly available, and others who should not be, and so I cannot effectively use keysigning internally to manage relationships. This is because I don't want to upload every key I know about to a public keyserver.

Maybe I am mistaken or maybe there's a way to do that without having multiple keyrings or something, but that's kind of the problem. It's really hard to tell what I would or would not be sharing because there's no "interface" to speak of and I am hardly an expert.