Joining strings versus augmented assignment

[Andy Todd]

In his Linux Journal piece on Quixote
(http://www.linuxjournal.com/article.php?sid=6178) Greg Ward mentions
that when joining a series of strings together it is more efficient to
use "".join(listOfStrings) rather than += (augmented assignment).

I couldn't find any obvious references to this in the documentation or
in this group.

Would anyone care to explain why this is so to a poor ignoramous?

Thanks in advance,
Andy