> But I guess it makes sense since desktop developers need to be able to see the mobile site sometimes.

IMO this isn't a good reason. Developers can change the user agent.

(I also imagine there could be a no-redirect preference for logged in users. Or even just a special query string you could add to the end of a url.)

You would just change the dimensions using the browser devtools no user agent faking needed

	▲	eru 7 hours ago \| parent \| next [-]
		I'm not sure dimensions are all that's different? Your website might want to present a different interface for people using mouse and keyboard than for people using tiny touch screens? Even if the number of pixels in the browser window is otherwise the same.
	▲	Wowfunhappy 7 hours ago \| parent \| prev [-]
		I think Wikipedia redirected based on user agent, but yes, whatever, point is if you're a developer you can use the browser devtools to simulate whatever you need.