I inherited 100k LoC "documented" by an LLM.

LLMs can put into words what a programmer can infer from struct definitions, function signatures, names and even taking a cursory look at a function body.

LLMs cannot retroactively find out the _why_ of design choices. If you don't document the reasons behind decisions while making them, they'll be lost, which is exactly what leads to superstition. As a result, changing code is error prone because you never know when code is written in a particular way for a good (and still valid) reason or just because.