I ran accross php value, php flag, php admin value and php admin flag in a couple of .htaccess files, and I've used them sometimes as well by just pasting an example, but I've never really understood why there was such a great diversity. Couldn't php_setting X Y just handle it, and if not, what do the admin, value and flag attributes mean?

explained

So one time when I had nothing to do I figured let's end the doubts once and for all, lets google :) And here's what I found:

php_value name value
Sets the value of the specified directive. Can be used only with PHP_INI_ALL and PHP_INI_PERDIR type directives. To clear a previously set value use none as the value. Note: Don't use php_value to set boolean values. php_flag (see below) should be used instead.
php_flag name on|off
Used to set a boolean configuration directive. Can be used only with PHP_INI_ALL and PHP_INI_PERDIR type directives.
php_admin_value name value
Sets the value of the specified directive. This can not be used in .htaccess files. Any directive type set with php_admin_value can not be overridden by .htaccess or virtualhost directives. To clear a previously set value use none as the value.
php_admin_flag name on|off
Used to set a boolean configuration directive. This can not be used in .htaccess files. Any directive type set with php_admin_flag can not be overridden by .htaccess or virtualhost directives.