tedster - 6:08 pm on Jun 14, 2010 (gmt 0)
The only real argument is one of what is practical in a real-world situation. For instance, a "www" canonical fix is in place across the domain and then one bit of content actually gets moved to another directory within a very large infrastructure.
Any backlinks that need the canonical fix will go through an "extra" hop -- unless you've got the resources to hand code each individual case. And on very large websites, those resources may just not be available.