Mike Kay's tip 8 how to use XSLT efficiently

Hi,

I've just read the eight tips how to use XSLT efficiently in the FAQs
(http://www.dpawson.co.uk/xsl/sect4/N9883.html#d12718e144).

But I have a question about tip number eight:
"Split complex transformations into several stages."

What does this mean? Is this a suggestion to apply multiple transformations
sequentielly in a pipe? What is the reason for doing this? Does some small
stylesheets perform better than one big one?

Thanks,
Peter