I once spent an entire day researching North American climate, flora, and wildlife as typically seen in a month's span at a particular geographic region of the country.

For the scenery in a single event of the story.

For an unnamed city in a very vaguely specified location.

For fanfic.

I also have about three books on blacksmithing and pottery-making sitting on my shelf due to a character in another story (who was, I might note, a demigod, and thus could have rightfully glossed right over the practicalities of these arts). I have not yet reached your level of commitment, but by golly, I'm heading that way.