Oils that cannot be preserved for a long time, such as vegetable oils, are partially hydrogenated in order to preserve them and lengthen shelf life. There is absolutely no health benefit that comes with this process, it is simply a means of preservation. Manufacturers do this so that they are able to sell less expensive oil and food products and keep these items on their shelves longer. Vegetable oils are cheaper than natural oils from animal fats, but vegetable oils spoil more easily. That's why they do this.
The result of this is the development of harmful trans fats. The trans fats in partially hydrogenated products are what cause bad diseases like diabetes, obesity, and clogged arteries resulting in heart problems.
So in actuality, naturally saturated oils such as lard, beef fat or butter, and tallow are actually better for you and don't contain these harmful trans fats.
Vegetarians or vegans can use palm oil or coconut oil as these are not partially hydrogenated.
The alternatives are slightly more expensive, but they are well worth it. I have written a detailed hub on this subject if you want to get more into the mechanics of it, read "A Big Fat Lie!"
Hope this was helpful.