the “what” is interesting on interfaces or when you generate documentation with some tool like sphinx or javadoc.
the “why” is interesting when you are somewhere inside a class or function and do something in a “strange” way, to work around a quirk in the codebase or something like that, or when you employ optimizations that make the code harder to read or atleast less obvious why somethings are done.
“previous entries” are previous entries in the discussion thread series.
but atleast for doom 1, 2 and 2016 i can say that the ost gets me pumped, so there is that :D