Two functions doing the domain mapping?

My client is doing the first site that has a separate domain, as opposed to the sites being accessed through a subdirectory. The setup and use of this plugin worked just fine! But, then I noticed that the Network -> Sites -> Edit Site also has a place for the domain name for the new site.
– Do these two functions collide or work together or perform different functions?

Thanks!!!

http://ww.wp.xz.cn/plugins/wordpress-mu-domain-mapping/