For example, Stripe uses a three-column layout: a navigation pane, a column to describe the API, a column with examples and error codes (see [1]).

In contrast, Mailgun uses two columns: a navigation pane and a colum including the API description and examples (see [2]).

Both layouts seem popular, and I'd like to better understand what's making you prefer one over the other. I'm talking about reference documentation, assuming there's also a separate user guide.

Personally, I find the three column layout harder to read: the example pane often wastes a lot of space and squeezes the actual documentation in the middle. On the other hand, I see more and more sites (and tools [3]) using that layout, so that's probably just me?

Thanks for your thoughts!

[1] https://stripe.com/docs/api

[2] https://documentation.mailgun.com/en/latest/api-sending.html

[3] https://github.com/lord/slate

(edit: simplified the layout descriptions)