>> Isn't the effect of "make extraclean; make" to rebuild Emacs with the 
>> default configuration options (contrary to "make bootstrap", which uses 
>> "bootstrap-clean", and with which the configuration options are kept)? 
>> Am I missing something?
>
> I'm not quite sure what you're asking here, so I may be missing 
> something.  :-)

😉

>
> After a "make extraclean", there's nothing more to remove, so saying 
> "make" or "make bootstrap" are identical in effect. So there's no point 
> in advising people to say "make extraclean; make bootstrap".
>

Exactly, so I think neither of use missed something! 😃

My point here is that this advice will be displayed after a failed make 
bootstrap, and that just telling to use "make extraclean; make" is not 
clear enough, its effect might be surprising (e.g. the toolkit could 
change from Lucid to GTK).  Given that its effect is to rebuild Emacs with 
the default configuration options, the two possible wordings are:

run "make extraclean" and run "make" again, to rebuild Emacs with the 
default configuration options, which might fix the problem

or:

run "make bootstrap configure=default", to rebuild Emacs with the default 
configuration options, which might fix the problem

Those two commands are equivalent, but I find the latter clearer, and it's 
not obscure, it repeats something that can already be found in 
INSTALL.REPO.