Generally, printing at finer layer heights brings more details out of the 3D model.  For example, if you have a complex shape such as an animal, you will see much more detail when using a .1mm layer height as you would with a .4mm layer height (four times the detail on the Z-axis).  Things such as the eyes, ears, and feet, will be much more detailed along the z axis with the finer layer height.  Remember however, that the finer you go on layer height, the better leveled the bed must be (new versions of Slic3r help compensate by allowing you to lay down more plastic on the first layer).

Before changing all your print heights however, there are several factors to consider.  First, the general rule is that the maximum layer height for a given nozzle is 80% of the nozzle diameter.  Therefore, with a .5mm nozzle (standard on AW3D v.5), your maximum layer height would be .4mm.  Indeed, we print out the Gen6 cover at .4mm.  The other parts however are printed out at finer layer heights, going down to .15mm for the herringbone gears (to pull out the resolution on the herringbone pattern on the Z axis).

Another consideration is print speed.  With finer layer heights, each layer will take the same speed, however, there will be more layers for smaller layer heights.  A .1mm layer height part will take 4 times a long to print as the same part printed out at .4mm.

Finally, when you go too fine on the layer height, the extrusion may simply be too slow to get accurate feed through the hot end.  On the .5mm nozzle, the minimum layer height should be .1mm to achieve optimal results.

in Working With 3D Models