It's things like these that are leading me to work on a Drupal book for the non technical, for producers and editors. I'd love encouragement, recommendations and book deals. :)
After dropping boiler plate language into a proposal regarding design and templates I recently had a great conversation with the proposal's recipient on what exactly a design was, what a template was, and how they related to pages in a Drupal site. Here are some thoughts on what templates are and what they offer.
If you looked through a magazine like Rolling Stone or National Geographic, no matter what page you flipped to, you'd have cues that it was Rolling Stone or National Geographic. This is the style. Aspects like footers that appear in the same place or headers that are consistently placed with the same type treatment can be templatized. Other consistent features, such as body text or call outs or captions can be captured online in styles in CSS (related to HTML/XHTML in case you're unfamiliar with the term). Anything else can be in a style guide, which isn't coded but is a handbook for maintaining a consistent look (such as http://www.uvi.edu/pub-relations/pr/branding/pdf_files/UVI_Brand_Style_Guide_7_sm.pdf [1]).
A template, then, is a precoded embodiment of consistent elements that will likely appear across multiple pages. In the magazine example, this would translate to the cover, table of contents, first article page and article page. Each of those would be templates, reusable, consistent yet customizable in parts.
Another client told me some of his staff had not understood templates very well and wanted a great many of them, not knowing that templates are really just collections of templatized elements. Templates should really be thought of more like Legos, with interchangeable parts, rather than something locked down.
And not all aspects of a site need a template designed. If a 'most popular content' block will look the same, other than it's text, as a 'most recently added content' block, then that block can be designed under a higher level name and generalized to be relevant to both, like Content List Block. Alternately, if something is definitely a one-off, something that will happen once, don't bother making a template for it. Just code it for that one instance.
The benefits to templatizing are consistent user experience and ease of content preparation for editors. On the negative side, excessive templatizing of a site can make it inflexible, boring and predictable. The less templatized the greater the burden on the editor to design and code and the more time they'll need to prepare content. Additionally, unless the editor is a skilled designer and coder, the finished product may have more variety, but will likely not come across as highly professional.