True, if you are using a shorter focal length you can intrude into the subject's personal space but here is a case for using a shorter lens, a 50-60 mm in Craig Tanner's "The Mindful Eye" a very informative two part critique of a portrait taken with a shorter lens.

http://www.tmelive.com/index.php/articles/view/759.html

Hope you can see that without signing up but if not, it's worth the trouble to do so.