[ear1grey]

The words “tag” and “category” are merely different specifications of a generalised mechanism for grouping posts. In some implementations grouping is user editable, in others it’s purely an administrator task. The former is often described as tagging, the latter categorizing. It’s most common too for tags to be flat, but categories to be hierarchical, but again this is more of a result of the reason for the implementation.

My opinion is that both tagging and categorisation are the same thing – they’re just examples of grouping, with different control mechanisms.

Grouping facilitates what psychologists call chunking (the formation of memory structures for perception and meaning), so yes, there really is a definite measurable benefit to tags and categories. The interesting bit is how you measure the benefit and separate it from the other factors such as how page layout can make the tags more or less comprehensible.

Currently in bbPress “forums” provide a single level of grouping (akin to simple categories) and tags provide unstructured flat grouping, though I’ve suggested in another thread that there may be an alternative solution which combines both for increased flexibility/benefit.