S3D has a steep price and it is often debated whether it is worth the money or not. Considering the fact that the company is in business for quite a few years, one can conclude that either it really is worth the money or alternatively there is an unending supply of (knowledgeable maker) fools who are easily separated from their money. Take your pick.

Apart from all that noiseboy72 mentioned above, S3D also allows you to define multiple profiles for different parts on a tray of parts to be printed together, allows you to define multiple profiles for different heights of you print, etc. Also, you can store the parts (stl) plus all the printing profiles applied to them in a single factory file. I use that a lot to save complex (trays of) prints so that I do not have to keep track of all the nitty gritty details per part or need to save hundreds of different printing profiles and remember which one to use for which part. You can view a factory file as a time-frozen archive of the parts and how to print them correctly (temps,speeds,layer heights,bridging,infill,etc,etc,etc, all of those able to change for the part/layer height), all in one self-containing file. If you need to re-print something just load in the factory file, slice and print. If you need to tweak it, load in the factory file, apply the tweaks (save the factory file again if needed), slice and print. It makes printing life a lot easier in my experience.

If you are a hobbyist with few parts to print, then I would recommend Cura or Slic3r which are both free and pretty good. If you are into 3d printing big time, then S3D is a must (my two pennies worth of advice).