PFPX sometimes produces unusual flight plans and issues SIDS which you wouldn't normally learn about in real life. But only if you let it find a route for you. It is only as good as the FMS data put into it. You could probably paste a route from simbreif into PFPX and force it to fly a better, more, realistic route. I do this with vRoute and it seems to work. But only if the FMS data is synched up, and I use Navagraphs FMS manager for this. As said before it isn't a flight planner alone. It is a flight dispatcher.
It seems to simulate a flight and keep your reserve fuel intact. PFPX has weather prediction. Bear in mind that ASN or VATSIM, IVAO, will have there own weather. I think PFPX weather prediction pretty good, even if I am using other weather programs.
You can export it all as a PDF. You can save route straight into the FMC as an rte file or most formats. Or you can save a p3d/fsx file and load that into Active Sky Next, and use the briefing section of active sky, for all the meteorological information regarding a flight. There are a lot of tools which are useful.
If anything PFPX is worth having more than TOPCAT, and I remember TOPCAT is now more integrated into pfpx (if you own it). TOPCAT is important, but it is just a T/O and Landing calculator. It is a small part of the bigger picture, in a flight operation. So personally I don't spend too much time on it.