Bad side: Allow to intrude privacy of the including script.
What one could have for information is the server address (eg.:
www.site.com) and not the full URL to the including script but $PHP_SELF
already does that so there is no need to go further than that IMHO.
In fact it would be handy then to have a include_history_disallow(),
to disallow included pages below the file calling this function
to access this information (then you´d optionally
need to save which file(s) sets this flag, because this setting should not
affect files which above and actually including the page set sets this
flag.