If you do not alter the propotions of a poly in UV space compared to its propotions in 3D then do not expect to see any effect by using the tool.
A way to use it:
First generate a UV map.
alter the dimensions of a poly in texture editor.
Next, select this and its neighborouring polys.
run the relax tool, you will see the vertices moving
I hope this helps,
modestos