Depends on what you're doing. I've used calculus for physics simulations in games. I had to do a bunch of performance analysis, and a little bit of knowing what distributions actually meant helped a lot. I regret not having taken more statistics in college. I was talking with a philosophy prof once, and somehow we got to DeMorgan's theorem. "I use that nearly every day," I told him, and it kind of floored him -- appa…
I used DeMorgan's laws when refactoring Boolean expressions for clarity long before I learned that the laws had a name - they're entirely obvious and self-evident. I think the relative pointlessness of specifically classifying and naming them makes knowing of them by name obscure.
If you're working with educated people, it's a lot easier to say, "apply DeMorgan," than to say, "why don't you negate the clause, remembering to negate each of the internal clauses, and switching the and's to or's and vice versa."
There exist people who use the names to sound intellectual, and these people are annoying, but just because some people enjoy spouting (in the general public) "obscure" rules and names, that doesn't mean that using such names is without value.