"Recalculate Normals: will force any two faces that have an angle larger than the crease angle to appear to have a sharp edge.
If the angle is less than the threshold the edge between the faces will appear to be smooth.
This is accomplished by creating or removing normals at the face edges. No vertices are created with this option.
The crease angle ranges from 0 to 180 degrees. If it is set at 0 then all the faces in the model will appear flat.
If it is set to 180 then all of the faces will appear to be smooth. Smoothing only works on faces that share edges.
If two faces seem to share an edge and smoothing does not change their appearance then most likely the edge is not shared and each face has its own edge.
To fix this you can weld vertices (PoseRay will suggest to smooth when you check on weld vertices).
As a general rule organic-type models should use 180 degrees and mechanical objects should use less than 90 degrees. There are 4 methods to calculate normals:
Normal sum calculates the normals at each vertex by direct average of the normals from the faces sharing that vertex.
Angle-weighted sum will weight the average according to the face angle at the vertex. (This method usually gives the best results)
Unique normal sum uses the unique normals at each vertex to calculate the average.
Inverse area sum weights each normal at a vertex by the inverse of the area of its face."
From here:
https://ca217bf218386ade28595be56ca98f5ee45ce5d2.googledrive.com/host/0B0MYeki9vLYYLXQzcVVua0lST2s/poserayhelp.htm#Vertices_and_normals