The factory-preload contains just about everything -- except the Xcode development tools and some other specialized stuff (that can be loaded from the install disks). I'm not aware of anything on the factory-preload that's "missing" from the install disks.
If you do a custom clean-install, you can arrange to "lose" several GB of bloatware, multi-lingual documentation, and unused applications.
For example, the iWork and MS-Office "Test Drive" bloatwares consume about 2.5 GB of disk space (that's OVER HALF of /Applications, in total). Also, if you don't plan to use them, you can save hundreds of MB by not installing big apps like iWeb or GarageBand. (You can easily install them later, if the need arises.)
Eliminating extraneous clutter speeds up the install AND improves system performance (especially file searches, Repair Permissions, SW Updates, etc). Lean n' mean systems run faster and are easier to maintain.