Symphony.

I'm storing my output xhtml templates in static xml files. Is there a reason not to use the document() function in my master.xsl rather than having to add my templates as a static xml datasource to every page on my site?

It's probably ever so slightly faster to use a document() call than include a Static XML DS, so long as those documents are local. The real benefit of this will be seen when they are only used sometimes, e.g. within an <xsl:choose>.

However, I think one medium-sized document will load faster than several small ones, so it depends on the size of your templates and how you're using them. It might be better to put them all together in a single file.