Now that I know which kind of postwork you mean, I think that it's extremely common, and, even with the greatest render engines, almost always necessary.  Poser Firefly doesn't have post FX built in, like some other render engines (Octane, Luxrender, MentalRay, Vray).  It can't do spectral bloom, glare, lens flares, aberration, or other camera lense effects, directly in the engine (that I'm aware of).  These other render engines can.  However, even with post FX in these other engines, I still find it useful to tweak some color levels and add some gamma adjustments to the resulting render.  No raw render is ever going to be perfect.  Even the highest end studios spend hundreds of hours compositing and color grading CG renders for major film productions and game cinematics, so I'm sure there's no amateurs out there who couldn't benefit from that as well.  I don't believe in the perfect render.

That said, it's rare nowadays that I spend more than a few minutes on post color correction.  So the raw renders are very close at least.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.