Hydrogenation is used for two main reasons primarily, to texturise vegetable oil to make bisuits (cookies) and pie cases and stuff. If you come across a biscuit without hydrogenated fat used in it (for example and organic one, damn sure it'll be a bit soggy.)
The other use of hydrogenation is increase of shelf life, this is to do with the process, which basically is when small amounts of hydrogen is added to vegetable oil using metal rods using catalyst metals like nickel and cobalt. Its cheaper than using lard or other hard yellow/white fats too.
In a regular fatty acid the hydrogen atoms mostly form a double bond on the same side of the carbon chain. In hydrogenation this is re-configured and of the double bonds that do not become chemically saturated, the carbon atoms end up on different sides of the chain. This is where the Trans bit comes from. 'Trans fats'.
If the hydrogenation process was 'finished' then the end product would have no trans fats at all, but be rock hard.
Anyway, as you know the H fats are associated with all manner of things from coronary heart disease to cancer to
lots of other health implications, its not well documented the effect on the body compared to regular unprocessed fat sources.
Fractionated oils on the other hand don't seem to be so bad, from a scientific standpoint, fractionated fats are considered 'natural' because fractionation is a physical rather than chemical process. Their main use over the years has been in cosmetics and stuff like that.
Essentially it (fractionation)is the process of separating some oil into two (or three or more) triglyceride fractions, also read....high-melting and low-melting fractions.
Fractionation is a more expensive process than hydrogenation though, and in essence does not produce trans fats because it is merely seperating the hard and soft fractions of the fat. It would be wiser to look at the source of the fat, for instance palm oil and similar and evaluate that. Obviously some oils are they way they are processed in themselves are better than others.