Why "Do not allow a dumped Emacs to be dumped" in [Emacs-diffs] trunk r116823

[scheme gentoo]

In this commit [1] seven month ago, changelog says "Always
prohibit dumping a dumped Emacs".

I don't understand why.  "/usr/bin/emacs" is already dumped from
temacs, so this commit prohibits me from dumping "/usr/bin/emacs"
again.  But as emacswiki [2] said, dumping emacs can greatly
reduce emacs start up time.  And I don't see any disadvantage of
dumped emacs (trunk version with this commit undo).

I think this commit should be partly reverted.

Jia

[1] http://lists.gnu.org/archive/html/emacs-diffs/2014-03/msg00212.html
[2] http://www.emacswiki.org/emacs/DumpingEmacs