Tinning is not presently a very useful skill. It is a passive skill that does what it is supposed to and helps keep a tinning kit from breaking when you tin a monster’s corpse, but the functionality you get isn’t really helpful. Food is easy to get if you need it, many races can just plain eat corpses, and a lightweight shovel is the preferred means to bury corpses when needed. Once in a while you’ll get a special tin that heals you, but it’s really not worth it at this time.

The ingame help reads:

Skill duration: random.
Type of skill : neutral skill.
Affecting stats: De.
It uses no endurance points.
One of the greatest, neverending need for almost all
creatures, is the need for food. Unfortunately, carrying
a slain corpse around is not a very tasteful or easy 
way to keep food at hand. Anyone who needs to survive
for a while and provide a practical source of food for
himself, learns to skin the corpses and refine the flesh
and store it in containers, where it is much better 
enjoyed, especially in the future. The more skillful
one is at the art of tinning, the better the quality
of the food he can store. Also, proficiency is needed
in order to not break a tinning kit.