What exactly is the mod rewrite part for?

Hi,

The following lines are added to .htaccess:

<IfModule mod_rewrite.c>
RewriteEngine On

RewriteRule ^wp-admin/includes/ - [F,L]
RewriteRule !^wp-includes/ - [S=3]
RewriteCond %{SCRIPT_FILENAME} !^(.*)wp-includes/ms-files.php
RewriteRule ^wp-includes/[^/]+\.php$ - [F,L]

And another 20 or so lines.

1. What are these for in terms of security?
2. Can they conflict with the standard WP mod rewrite a few lines down:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

3. How can I remove these?

thanks!

http://wordpress.org/plugins/better-wp-security/