Here is a quick test from me. Camera inside a shed with a window, no lights, purely lit by EZDome. The shed uses the standard PoserSurface in the material room. Rendered using Superfly. They are straight jpg exports from PPro11 at 100% quality. The only difference between the two pictures is the first one had diffuse bounces set to 0, the second set to 10 (highlighted in red in my render settings pic).

Using my gpu (GTX 980ti) the 0 diffuse bounce render took 159.24 seconds.

The 10 diffuse bounce render took 411.63 seconds.

To me this shows the difference between 0 and 10 is and for me worth the extra time.