you often need parts of a compiler in other projects. be it parsers for config files, implementing your own regex engine, to evaluate mathematical expressions users put in, parsing natural language input, etc.

it's nice to know some compiler theory. even as an autodidact. (which I am too)

but don't worry the basic stuff is really basic. it gets only complex when you try to optimize or employ some sort of "smarter" parsing than LL(1). and for that there are bison and friends.