The Main sliders For the majority of use, you will probably never have to go past this section of the dialog. The Detail slider controls how many pieces the segments are broken up into.
High detail carries with it high facet count, so be careful.
The Quality slider controls the rendering quality of the lightning bolt by controlling the number of facets in the mesh. You can see how the slider controls the facet count by looking at the Preview window. The Amount shown slider controls how much of the bolt is currently visible. This is useful in creating the illusion of bolt movement by only showing a certain percentage of the actual bolt. The amount always starts at the source and works towards the target.