The Translucence component in the PoserSurface material definition is the complete equivalent of the Ambient component, except that Translucence is available through the Advanced interface only and in various cases is not exported or translated to external renderers or materials definitions, while Ambient is available in the Simple and Advanced interfaces and in far more cases is exported or translated decently to external renderers or material definitions. So for those reasons, Ambient is preferred by most people.
Why having Translucence then? Well, it’s a kind of service for those who want to separate real-life object glow as it appears by led-lights of phosphorescence from faking real-life translucency (as it appears in wax candles, human skin and rice paper walls) by some sort of body glow. They can put the first effect in Ambient, and the second in Translucence. This second effect becomes obsolete though for those who use the real thing instead: sub-surface scattering as recently build into Poser.
human skin translucency, light scattering through ear tissue.