I wrote a long time ago, about /technical-writing/atomicity which (more or less) is the same as topic based authoring. Both describe the process of breaking information into the smallest coherent blocks and then using the documentation toolkit to compile the kind resource.
Topic based approaches to documentation promise reduced maintenance costs and greater documentation reuse. I'm not sure if anyone's used "ease of authorship," as an argument in favor of topic based approaches (they're conceptually a bit difficult for the author,) but you get the feeling that it was part of the intention.
The obvious parallel is object orientation in programming, and I think the comparison is useful: they both present with optimism about reuse and collaboration through modularity and modern tool chains. While object oriented programming predates topic based authoring, both have been around for a while and even if you aren't an adherent of object orientation or topic-based authoring, I think it's impossible to approach programming or documentation without being influenced by either of these paradigms.
Unless you're working with a really small resource, without some topic-based you end up with redundant documentation that looses consistency and a maintenance nightmare.
The downfalls of "topics," don't negate it's overall utility, but they are significant:
- topic based authoring makes it harder for non-writers to contribute to the documentation. This makes it more challenging to keep documentation up to date and can hurt overall accuracy.
- topics force writers to focus on the "micro" documentation at the expense of the "macro" documentation experience. The content is clear, the completeness is good, but the overall experience for users is awful.
- topic-centrism sometimes leads to deeper hierarchies which leads to duplicated content across the hierarchy as "cousin" nodes address related concepts.
What's the solution? I'm not sure there is a single one, but:
- it's important to avoid duplication, by having great support for "single sourcing" (inlining/inclusion,) and simple cross referencing.
- isolate all content in concrete topical units.
- start with flat global organization and add interpage hierarchy only when necessary.
- use as much intrapage organization and hierarchy as you need, and allow intrapage hierarchy.
- build great reference material first. Everything else is gloss, and you should layer the gloss on top of strong reference rather than try and build reference under an existing structure.