Thanks for the explanation about why C-h is needed for an
experienced user. I think however that enabling the help only for
the state when the search string is empty would be confusing.
I would prefer a defcustom to enable/disable isearch-mode-help on
C-h instead. Could that satisfy experienced users?
A key definition is as simple as defcustom. Instead of:
(setq isearch-bind-C-h-to-isearch-mode-help t)
you can put in .emacs:
(define-key map "\C-h" 'isearch-mode-help)
The main question is what should be the default. For novices, who
don't know how to configure Emacs, the default binding of C-h to
`isearch-mode-help' is very helpful. More experienced users can
put in .emacs:
(define-key isearch-mode-map "\C-h" nil)
if C-h is bound to `isearch-mode-help' in isearch.el by default.