Decarbing is only for edibles. If you're going to smoke or vape something it does not need to be decarbed because decarboxilation will happen when the matter burns from smoking or gets heated up during vaporization.
Buds naturally contain the inactive THCa, which turns into THC under heat, and THC is what causes the effects we're looking for.
If you don't decarb cannabis at some point before you eat it, you won't feel much of anything because it will stay THCa in your stomach, and it'll pass through without a whole lot of effects. If you decarb first you'll get THC delivered to your stomach and get the full effect.
As far as dry ice hash, it's pretty similar to dry sift in the end. You've basically removed all the trichomes without cooking them. If you're going to eat it afterwards, you need to cook it somehow, whether you make butter or oil, etc, or put the hash in candy or edibles.
If you don't want to make hash, you can​ make butter or oil straight from the plant matter. ​​​​
I personally use straight plant matters when making edibles because you skip the step of making hash, but still strain out all the plant matter during the oil or butter making process. I make hash for sprinkling on bowls. However, straight hash gives you slightly different effects (whether smoking or eating) so it's fun to experiment with what you like best!
