Any. Even if you're doing a blue collar job, understanding the fundamentals (or at least the specifics about a particular subfield) makes you "the guy" and adds

Any. Even if you're doing a blue collar job, understanding the fundamentals (or at least the specifics about a particular subfield) makes you "the guy" and adds some job security. As a programmer I often got ahead just because I'd read all of the C standard library, the Windows API docs, etc.