Ok, old POE standard in my head, but 100W is still only a handful of fixtures on a circuit.

Not an issue with PoE since you're running a cable out to each device rather than linking them in a loop/circuit.

But then that highlights the problem with trying to PoE and entire house - You have to run a line out from a PoE source to each item you want to deliver power to, and provide a port for each which comes at some cost. I guess you could try and run some kind of PoE passthrough circuit arrangement like you see with some office voip phones...

Complicated.

Modern fluorescent and LED lamps are around 10-15 Watts. So you could run 4-6 of them on a circuit.

The other thing is price out Ethernet cable by the foot and compare with 14g Romex. The former is $0.05/ft vs $0.20/ft. And you don't need a licensed electrician to run it.

Also PEO is low voltage and power limited, so safer.

That's ten 10W LEDs which is enough for most moderately sized rooms, and you can just run another cable if need be.

I gotta imagine 100W PoE requires some bigger cables than plain-jane Cat5E or even Cat6, though...?

The main design goal is to use normal cables. It's half an amp per wire max, which works out fine.

The higher power levels require that you take into account how each cable is going to safely dissipate a couple watts, which is easy if you're not running big bundles.