Nowadays a SEO is important for a good ranking in search engines.
Google and many other search engines can tag your index page as duplicated if they find that the same page is showing when they go to:
http://www.yoursite.com
or
http://www.yoursite.com/index.html (or index.php, etc.)
To avoid this you can use the following rewrite rule in your .htaccess file:
RewriteEngine On
# Remove index.
RewriteCond %{THE_REQUEST} \ /(.+/)?index(\?.*)?\ [NC]
RewriteRule ^index.html$ http://www.yourdomain.net/%1 [R=301,L]