Personally, I like knowing how rare items are (as in how many copies exist of it). It's also good if you during a loot of a corpse, since you can essentially see how good items are quickly. Lastly, if you're exploring, it's nice to have it up to see if it's worth fighting a mob for their item.

Or, you're just l33t and know every single item and its rarity, and you dont need this BS. But if twist uses it after he kills someone, that's a good enough reason for me.

Here is where I'll insert my own gripe of how some of these skills you gain from obs/exp, etc. require that you actually learn them first. I feel like it's just an unnecessary disadvantage for low-int races who can't afford to spend practices on these.