[tripzilch]

Another use case for me is that I can more easily route audio from sources and applications to other applications, using JACK (and Patchage as a GUI).

[microcolonel]

This is not too difficult in PulseAudio. Every output has a "monitor" which can be routed to any application that's recording. You can do this through a GUI called pavucontrol, though it's not as pretty or flexible-looking as patchage or many of the other JACK patchbays. PulseAudio is, of course, more geared toward consumer and basic professional scenarios in general. Synchronization becomes important once you're routing through a couple of different applications.