Let's continue working with this object. Back to the geometry level (under the MeshSmooth modifier) go to Edge mode again and select the 4 side edges of our cube's frontmost section (for the Wireframe mode hit F3). Chamfer them 0.1 units and have a look at the smoothed result. The corner edges can be clearly seen in the smoothed geometry.
Be careful with Chamfer. It can really mess up your geometry if you have some modeling left to do. This is why it is best to do all general modeling BEFORE actually starting chamfering edges. In this case I tried to extrude the faces in the middle. You can notice that the extrusion is clean to the back of the object, where no chamfering was done and it's messy to the front.
Let's go back to our cube prior to any chamfering being applied to its edges. Go to Poly selection mode ("4" key for shortcut). Select the polygons in the middle (use F3 to toggle wireframe On/Off).
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