Instead of open many buffers I wish to have the same buffer for all calls to the man.
Here's a function following @Drew's excellent suggestion:
(defun last-man-standing () (interactive) (kill-matching-buffers "^\*Man .*\*" nil t) (call-interactively #'man))
A couple of notes:
man's fancy guessing of which man page you want.
I didn't know that
kill-matching-buffersexisted, but since Emacs often has exactly the function you need I went
C-h f kill-match TABand sure enough, it was there.