Benefits of smooth stem over rough stem:
Smooth stem plants like guava, eucalyptus etc do have a smooth layer of bark over its stem that comes out as a skin when they shed their barks. Whereas most of the other plants like mango, banyan etc do have a rough corrugated layer of bark over their stem.
The smooth stem doesn’t let water to accumulate in the bark which can led to infections to the tree. It also doesn’t allow any seed to settle on bark that can led to growth of parasites. Thereby this smooth bark saves the trees from some of the probable harm to the tree.