Following on the heels of Alignment- and Class-Restrictions comes the decision regarding which sourcebooks to allow and which to disallow for players to use in selecting Classes, Prestige Classes, Feats, Weapons, Spells, and other details.
“Sourcebooks” may include :
- Official hard-copy published books of D&D v.3.5 material (or whichever RPG system you are playing).
- Hard-copy published sources, such as magazines or 3rd-party-written material.
- Official, published RPG errata.
- Electronic versions of books, documents, articles in .PDF or tablet/e-reader formats.
For the sake of simplicity or familiarity, as DM you may decide to set aside the entire content of some sourcebooks. The sourcebooks may contain material that is not related to your campaign’s theme or setting; may not fit the spirit of the adventure; or may be overpowered or unsuitable relative to the type of conflict(s) in your story.
The sourcebooks may be part of a specific D&D (or other RPG) “universe” which is not connected to yours. Shadowfell and Underdark books, certain 4th Edition module books, or RPG supplements (such as the various region-books published for the RIFTS game system) may not “bolt on” to customized aspects of your campaign and setting and theme.
It can be difficult for players and DM alike, if sourcebook material is available only in electronic format and is, for any number of reasons, not immediately accessible during the game. A player taking a spell or Feat from an obscure source like a 3rd-party website related to the RPG or from a .PDF copy of a sourcebook stored only on her computer at home, creates a difficulty for a DM who needs to rule on the interpretation of the spell or Feat’s effects but hasn’t got the source to use as reference.
Some sourcebooks may contain some or all material that has been revised or corrected in later versions of that book – or reworked and added to newer sourcebooks. Some skills, spells, and Feats from D&D v.3.0 and even D&D v.3.5 are good examples of this. Same too with some newer rule sets and changes in 4th Edition D&D. The DM should be specific about exactly which sourcebooks will be considered canon.
And of course there is also preference; some DM’s don’t like the content of some books or don’t see a place for it in their games. In terms of D&D v.3.5, one such discussion often centers around the inclusion or exclusion of Psionics. Some DM’s see mental powers as a normal addition to the fantasy setting and allow Psionics; other DM’s don’t feel that Psionics have a place in D&D at all. Framing your decision as a thematic choice may provide all the justification you require.
You may find that, ultimately, your choices of included and excluded source material is a reflection of the boundaries you wish to impose upon your campaign.