A graduate student from McGill contacted me recently to ask about my blogging practice with a focus on how I use categories within my blog. If you are curious too, this is my answer, edited for the blog format.
As with many blogs, I have both Categories and Tags. The categories are always listed in the navigation column. The full list of tags I've used at least a couple times are listed on my tags page (alphabetical list with sizing by frequency).
My strategy behind categories has always to cover the topics I like to think and write about most frequently. I generally don't delete or remove categories (what would I do with them?), but I do add categories as they are needed. For instance, when I took a new job, I created a category to capture articles related to that role. Articles can sit in multiple categories - and that seems to be the case more and more lately. I have experimented with categories and subcategories, but decided it was too confusing in the context of the blog. I don't think individual readers would "get" an structured categorization of topics beyond the alphabetical list.
The tags I use to expand on the categories and will contain the name of people or companies referenced, journal names, other topics, etc... This seems easier, and I wonder if a blogger starting out today wouldn't simply go with tags.
One thing I have thought about but never done is to review the heavily-used tags and consider whether they need to become categories. I am thinking of my "change management" tag - but then I use it in conjunction with other articles that usually get a category, so I am not that worried.
[Photo: "A Sketch Towards a Taxonomy of Meta-Desserts" by several bees - yes a taxonomy of desserts!]