To suit you. There are choices because nobody can tell you what
balance of quality and file size is right for you.
Above all, experiment to find your ideal settings.
Also, if you are using the Create PDF button, that makes much larger
PDF files than just printing to Distiller. Do you really need all the
interactive features like bookmarks, tags etc. If not, use Distiller
directly or turn of the features you don't want.
Aandi Inston