On Thu, Jun 05, 2008 at 08:51:46PM -0700, Junio C Hamano <gitster@pobox.com> wrote:
> In what sense is this "like show-branch --merge-base"?
> 
> The only similarlity I can spot is that it can take more than two heads,
> but what it computes and the way it computes it seem to be different.  It
> certainly looks much less efficient as it does not walk the ancestry chain
> in one-go like show-branch does.

Exactly. The original idea was to avoid the current limitation:
show-branch uses object flags for each branch, which is not something
that works if you have a lot of ones.