Being able to go all the way down the software stack makes it much, much easier to keep said stack honest. Debugging is often a desperate attempt at establishing ground truth. Without a low-level understanding, you're always a the mercy of your tools, and how they have decided to curate the information they're feeding you. Even the most well-meaning curation can be so frustratingly deceiving as to incite violence, and god help you if something you're interacting with has a smug sense of knowing what's best for you.

There have been a number of cases where I've had to rely on the ability to debug binaries directly at -O3, or to resort to Wireshark to get the dose of reality needed to challenge my [our] flawed mental model. If I hadn't been able to do those things, I'd probably still be there, pondering those defects, if not in body [due to declaring outright failure], at least in spirit.