this change does two things:
1) writes the css saved to a file in the plugin directory
2) enqueues it using wordpress template api instead of always adding it to the head
theoretically, it should improve load times since browserts can do their own internal caching of the css, and also plugins like Minify will be able to work their magic on the css code if employed.
as a side benefit, it will stop the generation of PHP warning messages like this:
PHP Warning: Cannot modify header information - headers already sent by (output started at E:\xxx\wp-content\plugins\imporved-simpler-css\improved-simpler-css.php:245) in E:\xxx\wp-includes\pluggable.php on line 866