I'd never come across process substitution before, very neat.

Some reading around suggests that it typically doesn't actually create temporary files as such, just multiple pointers to the same pipe.

And that in cases where it is achieved with actual files, those are deleted when they're finished with.

https://unix.stackexchange.com/questions/17107/process-substitution-and-pipe
http://tldp.org/LDP/abs/html/process-sub.html