Trailing slash at the end of permalink loads faster / better SEO?

If the permalink is to a file with an extension, no trailing slash is needed.

http://www.domain.com/afile.html

If the permalink is to a directory, a trailing slash is preferred. Otherwise, the server will respond with a redirect and the browser will have to add the trailing slash and make a second request automatically.

http://www.domain.com/adirectory/    is served immediately by the server

http://www.domain.com/adirectory     browser must make a second request with trailing slash