Engraver is the skill used for smoothing or engraving the walls and floors of your fortress. It is only possible to smooth and engrave natural walls and floors, not constructed ones. Engravers also carve fortifications into constructed walls. 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 also used to inscribe memorial slabs. Once a mason has prepared the slab, it can be inscribed with the victim's name at a craftsdwarf's workshop.
Engraving is a good way to gain experience. Smoothing improves your fortress, doesn't consume resources, doesn't create garbage and builds experience very quickly at the higher skill levels. It's also a wonderful way to utilize idlers, in a less-busy fort, for its low level of designating needed.
While experienced dwarves are more likely to engrave historical events than a novice, it is unclear if personality has any effect.