Separated uses can make sense in some situations

A big plank of libertarian thinking is that land use regulation is bad, that property owners ought to be able to proceed unfettered.  That means that you can put a gas station next to a house, or a school next to a fertilizer plant, even if it isn't a good idea.

Mostly, office, retail and residential can be mixed.  Universities and clean research facilities too.  Maybe even nuclear processing facilities ("Toronto residents shocked by local uranium facility" from the Toronto Star).

Probably not power plants, because the emissions have negative health impacts on some (this is an issue in DC, with a power generation plant owned by the US Congress, see "Use of coal in Capitol plant draws protesters" from the Washington Times").

Even hospitals, although their sprawling nature ("Gazette) and the fact that the high pitched sirens of ambulances going to emergency rooms can be piercing and negative in the context of "quiet enjoyment" of residential living.

But it's not a good idea to put housing and schools by fertilizer plants, chemical plants, and other "dirty" and dangerous industrial uses, as the West, Texas fertilizer plant explosion indicates.

Image from Daily Kos


And minimal and dis-coordinated regulation doesn't help (not unlike the same problem with delegating the regulation of so-called compounding pharmacies to the states).

 See "Fertilizer-Storage Risk Is Often Overlooked" and "Deadly Explosion Prompts Fresh Look at Regulation" from the Wall Street Journal.