There is no default page to open if the page name is not specified, is either " index.html " or " index.php ", with the priority assigned to the latter being the default. Thus, there will be no advantage as such, and moreover, it is not needed.
For any other page (except the "Home" or " index " page), if you specify a redirect header 301, then you tell Google and other search engines to save the destination URL as active and last (not the first) in their database . This is similar to setting up a permalink in search engine databases with the latest active URLs.
However, the advantage will be great . When you specify " http://www.mydomain.com/index.php ", you notify search engines to load the page " index.php " only all the time. However, if you simply indicated “ http://www.mydomain.com/ ” in the search engines, then this is before the interpretation of the server ( mydomain.com ) (after understanding the rules of the HTAccess server and other redirection rules, if any) to show the correct file for the user - it can be " index.php " (first priority) or " index.html " or " index.htm ", although this correct file may or may not be present on this server. If the file does not exist, the 404 Not Found page is displayed. And the responsibility of the owner of this server is that he has the correct file in his server root folder, so the 404 Not Found page will not be shown to anyone.
So, I will say that this is a great advantage saying " http://www.mydomain.com/ " instead of " http://www.mydomain.com/index.php ".
Hope this helps.