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I understand what you mean, but think of causal interactions as a fast, cheap filter.
Finding people you'd really like to connect to will necessary involve a lot of trial and error. You would like to minimize the costs (in time and effort) of the trials and the errors. Causal connections basically allow you to do this: you have a limited, surface contact with a person and in the majority of cases that will be enough for you to filter that person out and continue looking.
Don't think of small talk as a way to bond -- think of it as ritualized low-effort behavior one engages in while evaluating the other person.
I was in fact referring to casual interactions as way to bond and build rapport, because a lot of people do it that way, and I also think that's what MathiasZaman suggested (though maybe he meant it in a different way?).
Oh wait. Is that what you mean by small talk? I think my understanding of the concept just shifted. I was thinking of small talk as "that boring thing people do when they don't want to talk about serious stuff". But of course I use it in the fashion that you described, and it's actually quite fun when done that way.