I've used PXE (not even iPXE, just DHCP/TFTP without HTTP) mainly in environments where a LAN client-server game would need to be launched on many systems at once. Nothing quite like rolling out a hand-tailored distro for a single game to 16 computers and seeing them all boot and load straight into the game, one after the other, entirely unattended, from one broadcast boot-over-Ethernet trigger.

I think at one point we were even using distcc to use the clients to speed up rebuilds while iterating on the game. I should revisit that with iPXE and icecream.