I could not agree more: I once bumped into someone in the bathroom on a different floor that I had met briefly years before during a re-org meet-and-greet. In a few moments of catching up, I found out he had worked on an in-house project that was essentially the same category as the products I was on a team to evaluate.
We didn't end up resurrecting his project, but his insight into the ultimate selection and experience with the rollout was extremely valuable.
A similar thing for a casual acquaintance who told me in passing about his private work in app development, and I was able to put him in touch with someone on our app team (it was a big company with a lot of silos).
I ended up later working remotely for a few months with the same company, and lost the serendipity of accidental human interaction when all my communication was low-bandwidth, narrowly focused, topic-at-hand meetings and communication.
I can sympathize with others complaining about the high cost of interruptions, but for the way I work and think, non-directed conversation is invaluable.