Have you ever thought that you needed to add extra detail to your 3D objects and end up smoothing them so much that your great grandchildren would see the end result of your renders? It is an easy way out but on the expenses of render time. So what can you do to have a smooth surface and yet having a reasonable render time? Smoothing groups are the solution to your problems.
For the following technique to work, the editable poly modifier needs to be the lowest in the stack and cannot have any modifier (or the original primitive object) underneath it.
To see the power of this technique we are going to draw a simple cylinder in our viewport and give it 12 segments, with no height segments which would create 48 polygons.
To make it smoother at close range you would need to bump up the segments to something like 32 segments which will lead to having 128 polygons:
What if we want to have a low amount of polygons but still retain smoothness?
Return to the 12 segments cylinder, right click on it and convert it to an editable poly.
In the Subdivision Surface tab of the Editable Poly, check the Use NURMS Subdivision which will smooth it all together, like if you would be using a Mesh Smooth modifier.
Note: This technique can be done using a Mesh Smooth modifier after adding an Edit Poly modifier to the box.
Select the height faces of the cylinder and look for the Polygon: Smoothing Groups tab in the Editable Poly. By default, primitive objects come with the smoothing groups already defined for you. Select a smoothing group number for all the faces and then go back to the Subdivision Surface tab and check Separate by Smoothing groups.
This will create a smooth version of your cylinder with only 34 polygons.
Look for the next tutorial for more an advanced technique on the utility of smoothing groups.