if they contain php it is much easier to put them in static files.
What it boils down to is a cost benefit analysis, something like this
Cost:
storing in the database increases load time
Benefit:
updating the files is much easier, especially if a non-technical individual is doing it.
Cost:
it will take longer to program the database solution if you allow php in the templates
Benefit:
You can build an admin area that allows you to put the templates and plugins together very quickly.
