>
> I'm not opposing anything, but I wonder if mentioning of --first-parent 
> somewhere might be useful to others, because I find it pretty useful.
>
> This is why I am using it, all the time so far, in Emacs, which is 
> admittedly a small sample size:
>
> We have master with frequent merges from emacs-28.  If I know that a 
> problem exists in master, but not in emacs-28, or if I suspect that is 
> the case, I don't want to waste time checking commits incoming from 
> emacs-28.
>
> You have to know what you're doing, as always, and YMMV, and blahblah.
>

😉 I think the --first-parent is doing too much for your use case, because 
it will also skip other merges that are not from emacs-28.  Moreover git 
bisect is "fast", in a typical bisection only a few commits are checked. 
So I don't think that excluding merge branches without being 110% certain 
that the bad commit is not in these branches is a good idea.  That being 
said, I'm of course not against mentioning --first-parent either.