To render a realistic skin, you need to fake subsurface scattering. You would need that as well for realistic milk, orange juice or wax by the way. The real skin shaders try to simulate that, as well as the reflections skin gives. As far as I know the skin shader itself needs no ray tracing.

To get realistic light quite easy, you probably will use Image Based Lighting (IBL). You can set the mood of a scene very easy with that. But since you cannot use shadow maps with IBLs you need ambient occlusion, either on a light or on a material. AO creates a shadow if two surfaces are very close to each other. But Ambient Occlusion needs Ray Tracing.

You can get good results without IBLs, but it is more work. I need many test renders to get the light halfways to my liking, and I do use IBLs in most of my pictures.

Use manual render settings - the automatic stuff is not good. I use seven different render settings regulary - some with shadows, some without, some with ray tracing, some without. Different shading rate ( for most finals I use 0.0), different number of samples.  So I can test most aspects of a picture quite fast. The final render can run overnight - six hours should be long enough for most stuff.

On the other side - I have heard that movie companies mostly work with spot and infinite lights,  and use ray tracing only if absolutely nessesary. If you want to render a movie, short render times are very important, and PRenderman is much faster without GL and ray tracing.
See what works for you.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.