Saves so much time??? Really? You set up a dev env once, how much time is it even possible to save?

No, it's saving time because some things might work on one OS but not another, and then dealing with updates to each OS that might break something, or we need a new piece of software but it doesn't work on Windows for local development, et cetera, et cetera, et cetera. There are so many ways it goes wrong, I speak from personal experience.