I'm no expert, but I believe that hydrogenated oils are oils that are supposed to be unsaturated but are chemically altered to be solid at room temperature. Crisco shortening is a good example of this. Trans fat is just another name for them. "Trans fat" is a term that describes both hydrogenated and partially hydrogenated oil. They have slight chemical differences, but both are unhealthy.
As for pros and cons-
Pros to trans fats- Not many, but, they make food taste good and are more convenient for manufacturers to use in recipes. Naturally saturated vegetable oils like palm and coconut oil are expensive and spoil easily. There are no health benefits.
Cons-Because these fats have been chemically altered, our bodies do not know how to digest them properly. Instead of exiting the body, they build up in places like arteries, and we don't want that. They raise bad cholesterol and lower good cholesterol. This is also bad. Also, watch out for products that say 0g of trans fats on them. Most of the time they do have trans fat. They can say 0g because it is 0g per serving, and if there's less than .5g they can say 0g. So, what they do is make the serving size really small so they can slap the 0g stamp on the box to make it seem healthy.
So, my best advice would be to stay away from them. And if you're making pie crust or any other pastry that generally calls for vegetable shortening use butter or lard instead or find a trans fat free shortening made from palm oil.
