type is a characterization of content (post, static, gallery, …)
section and categories “sort” your content in different ways.
And now: Assuming I have some static sites (contact, about, and so on) and blog entries for different topics (photography, TeX, random, …)
In this setting the type is “post” or “static”, the layout changes on this type by an if statement (static content has no image).
Would you choose sections for the different topics or categories?
I guess it depends on how you want the site to be laid out, but I think the most common approach is to use “post” types for the blog while using taxonomies for the different topics.
I generally create distinct content types for my one-off pages like about, contact, etc. That allows me to create distinct layouts for those pages if I need to override the default page template.
different types for one-off pages and types are “internals” for layouts, …
classify content by tags and categories
What are you using sections for? Or is sections a kind of taxonomie? It’s hard for me getting these things sorted in my head in a “correct” way. Should I give up this approach and use everything just I think about it?
What is a nicer way for users? Getting every post by a scheme like domain.tld/post/single-post or is it useful to give the topic a chance to get there domain.tld/topic/single-post?