This script allow thorough customization of how you can defragment indexes and update statistics.
You can limit the size of the index (say you don't want to do a huge index except during scheduled maintance window, then do it manually). You can exclude databases, you can update stats, the list goes on.
At the heading of the SP there is plenty of documentation as to what things do and how to use them. Throughout the code, there are comments galore explaining my thought precess when adding that section of code.
I hope this helps