Machine room archaeology
The Computer Science department has been using its primary machine room for at least 25 years, and it's a proper machine room, complete with a raised floor. (People with the right sort of experience are now wincing.)
The problem is best illustrated by an anecdote: we just recently took out some hybrid 208V plus 120V power circuits that we believe were put in to power old Vaxes (which would make them obsolete for going on 20 years). We didn't have them removed out of any sense of neatness; we pulled them only because we needed the breaker panel space they were taking up for more plain 120V circuits.
(They were taking up three breaker spaces each, because apparently each hot wire uses up a space; 208V uses two hot wires, and the hot wire for the plain 120V was the third. My new job is an education in many things, electrical power issues included.)
The problem with raised floors is that over time all sorts of things accumulate down there below the floor tiles, because they aren't in people's way to be tripped over and thus yanked out. In fact, once you pass a critical snarl point pulling things out takes more work than leaving them there and just running new wiring over top.
By now, lifting up our floor tiles is an archaeological expedition into the dusty depths of our machine room's past. The CAT-5 tangles are the most recent stratum, then comes the carefully tied down runs of now obsolete serial cable that once connected to various consoles (we think), and down at the bottom you can still see the faded orange of a loop of thick Ethernet, complete with vampire taps and thicknet cables stretching off to somewhere. We're not sure what stratum the occasional dusty power cable belongs to, or whether they're still connected to anything.
(We are still better off than my old job, which once managed to accrete a slowly growing puddle of water until it seeped through a cinderblock wall and started soaking the carpet in my cubicle. Although to be fair, this can happen to anyone at more or less any time. That's the other problem with raised floors: you can't see what's going on underneath them, you just have to trust that nothing interesting is.)