On all most there is a High Detail and a Low Detail. This is mainly so it is easier to run on computers. If you have a older computer you should choose Low Detail and if you have a new or a computer that runs good you should choose High Detail. There is not that much of a difference.
High Detail-Better lighting
Better graphics
Less Bugs, Glitches, Errors
That is mainly it, but you may choose any detail you think you can handle.