Hey Wee,
You've correctly identified the two ways you can map custom XML data into Word. Here's how I think of each seperate technology:
- Custom XML markup is all about putting semantics to the presentation when the two are tightly tied (e.g. the whole document is a <book/>, the first 10 pages are a <introduction/>, etc.) In this case, you need to be able to mark up the presentation with semantics and the two are tightly coupled
- Content controls are all about cases where you have data in your custom XML schema that defines pieces of the file (e.g. the metadata table on the first page, or each of the issues in the file, etc.) and you want to create a mapping betweem the two - you live in and work on your data, and the presentation is outside the scope of your tools except where you've defined mappings.
The content controls do have additional granular control (i.e. editing/deletion protection, the ability to appear as common form controls, etc.) since they utilize the ability to be linked to seperate custom XML data. Hopefully this makes sense of why you'd use the two, and I'd love to hear your experience once you do.
Tristan