Food preservation is one of those quality-of-life wishes, just like wishing for Detect Item Status. You don't see it on the wiki because there are nearly always other options that give you more raw power, right away. The farmer corpse for an ultra ending is a special case, I believe they have a very high chance of dropping a corpse when the quest is active, even without Food Pres.

Preserving corpses for Guth'Alak can be done by 'cooking' them with a wand of fire and then blessing them. A blessed cooked corpse will last quite long without food pres.

Also, a lot of valuable corpses are Animals (blink dogs, giant slug), and you can farm their corpses with arrows of hunting that you can milk from barbarians in the wilderness.

But if you like the skill by all means go for it, sure.