Sections, Categories, and EntryTypes. Which, when? bit of a 'best practice' question, as I'm very sure there are many ways to do this sort of thing, but...

When/how do you decide whether to use a section, category, or entry type to organise your entries? I've been finding that my EntryTypes match 1:1 to the categories in my 'global' group, and that's lead me to wonder if there's any point in having them as global categories too, and whether I'm just not understanding how to use these tools properly.

For example, I've got sections: webDevelopment, generalWriting.

And categories (in a global group): Article, Tutorial, Links.

And EntryTypes in each section: Article, Tutorial, Links.

It's starting to look like there's little point in having global categories, but not having categories feels very weird / wrong.

So... how do you decide how to organise your stuff?
Sections are for completely separate areas of content. They have their own URLs, and are conceptually different. Like blog posts and press releases would be different sections. Your sections could easily be one section with a different set of categories defining web development and general writing. This is entirely up to you.

Categories are for separating entries into smaller groups. Your use of categories is correct. You just use it to categorize entries.

Entry types are when you have common content that require different field layouts. Think Tumblr and how it has one stream that shows text, pictures, links, and quotes as separate types. For your setup, if no entry will be both an article and a tutorial at the same time, you can remove the tutorial entry type and simply use the article one. Then in your template, use the category to decide how to lay it out. The link has a different field layout so it can stay separate.