Dark fibre is de rigeur for most campus applications--most of the cost of fiber optic cables is the installation, so it's not much more money to run 12, 24, or even 48-strands of fiber when you may only need 2 to connect a device in a closet.

So, in my situation, it allows me to put in new network equipment without having to take the old out, and just cut it over where the central backbone switches are with virtually no downtime. I like zero downtime.