There may be certain books that you want to designate as 'off-limits' to the players. Do you want to limit the players to only use a subset of the content you've purchased? For more details on the benefits of this approach, please see the article PC Ownership Versus Control. However, there may be reasons to prefer having all players use content sharing, as then all the PCs are owned by the campaign and can have control assigned by the GM. HLO implicitly supports a combination, and there is no limit on the number of PCs within a campaign that leverage content sharing, so a mixture is not a problem. Will all players be using shared content or will some want to use their own purchased content? When planning to run a campaign with content sharing, there are a few questions that warrant consideration before inviting players to your game.
