Well, it would allow a customer that does not pay for PHP to enable PHP for his web site (if he knows about .htaccess). The same goes for other features. He might even be able to switch off PHP Safe Mode, and that would be a security risk.
But you can take a look http://httpd.apache.org/docs/2.0/mod...reference.html
It will tell you what you need to put behind AllowOverride
to get your directives working.