your monster looks really similar to that on the movie: the only thing I remember good is the fingers of the hand are twisted around the wrist like the grasshopper as I read in an 'making of' article.
Practically, it walks on knuckles. But feel free to correct me if I'm wrong.
Anyway, it's a really good start, I like the head and the good fine sculpting of the palm.
For your question, the anser is: yes! The re-topology is used to create a lowres version of sculpted object to make things more manageable and clean when you think the sculpting is getting messy.
Thanks for the reply! Indeed the monster does walk on it's knuckles occasionally, but I based this mesh off of the images found in the extras of the DVD. I figured once I get the whole thing done and I'm ready to start posing him, I could transpose the fingers into that curled up "knuckle" position. I'll be working on retopology in the near future
I think you're right: even if it walks on knuckles, for modeling/sculptin purpose it's better your pose THEN a better pose, but not necessarily on knuckles.