Optilink avoids doing DNS lookups as a speed improvement, so what it does instead is to match the text of the URL. It attempts to find multiple forms of the target URL, but it is not perfect. For the target url xyz.com, Optilink will test www.xyz.com to see if it is the same IP address and looks like the same page. All internal pages on the target URL will also be loaded and checksumed and compared to the target page so we can usually figure out that www.xyz.com/index.html is actually the same link as xyz.com.
But there are some cases the program can not handle, which is what the 'aliases' list is for. You might have noticed that OptiLink automatically fills in the aliases it does find. You can add aliases as well for those cases where OptiLink would not be able to discover it.