Both seem to do the same thing, what is the main difference?
Hi David,
A lot of people have problems with this.
It depends on the resolution you set;
if an Edge is (much) too long for the resolution, Subdivide Edges will subdivide that Edge to get closer to the set resolution
if an Edge is (much) too short for the resolution, Collapse Edges will collapse that Edge, to make it longer, to get closer to the set resolution
Subdivide Collapse does both
Now, if your resolution is low (larger edge length than in your Mesh), no Edges will be Subdivided, so in that case Subdivide Collapse will do the same as Collapse.