[Filter actions] What does filters do?

I was using VIGOS Gsitemap generator and at the end of the file I saw 3 different filters


I'm guessing this is telling spiders not to count any index/htm* files as backlinks?

 <filter action="noindex" type="wildcard" pattern="*/index.htm*" />

Code (markup):

But what does these 2 filters do?

 <filter action="drop" type="wildcard" pattern="*~" />
 <filter action="drop" type="regexp" pattern="/\.[^/]*$" />

Code (markup):

 

I use http://www.xml-sitemaps.com to generate my sitemap codes and I think there are no filters there....