Engraver is the skill used to smooth or engrave rocks, as well as to carve a fortification into a constructed wall. The skill of the engraver does not affect the quality of smoothed tiles, but does affect the quality of engraved tiles. It is a good idea to train engravers by having them smooth large areas before engraving anything.
Engraving is a good way to build up the attributes: strength, agility and toughness. Smoothing improves your fortress, doesn't consume resources, doesn't create garbage and builds experience very quickly at the higher skill levels.
However, if engraving is a dwarf's highest skill, and that dwarf enters and completes a strange mood, then the dwarf will reach legendary status in engraving, instead of in one of the more valuable skills that are harder to train. If you want to build attributes fast, consider pump operating or record keeping as an alternative, as a mood will not result in a legendary pump operator or clerk.