"People do not write byte-code; that job is left to the byte compiler. But we provide a disassembler to satisfy a cat-like curiosity."
If I was an emacs fan I'd be weary of this. What happens if the devs are hit by busses? What happens to emacs? No documentation means very little stability.
Documentation of source code is often overrated IMO. Most software isn't difficult to understand if it's at least somewhat well-structured - and when the structure is poor, documentation doesn't help much.
It's usually the application domain that's hard to understand, because that's where global invariants and assumptions live.
(Don't get me wrong: documentation of module boundaries is great, particularly if there are many users of the module, up until you get to APIs, where documentation is essential for a decent experience. Documentation of the innards of software, not so much.)
O-code predates it by a couple decades for general purpose compilation: https://en.wikipedia.org/wiki/O-code
By the time it was implemented for emacs, many, if not most CS students would have been familiar with p-code as used for UCSD Pascal etc.
Of course, if you have Emacs you'll presumably also have the manuals. Chapter 16 of the Elisp manual seems pretty thorough.
On the other hand, developers losing will… The loss of Gmane, for instance, caused major link breakage for months.
Edit: If you consider DNS as SaaS then I also use that but I don't need it internally for my network to function so I won't call it a dependancy.