It is a fact of Pathfinder that the classes aren't perfectly balanced. While this may be fine in your game, it can often be disappointing for players who are stuck at the low end of the tier list compared to the rest of the party. By making minor adjustments to the abilities of the classes, you can adjust their power levels to improve the balance of your game.
Pathfinder - Gamemaster Resources
The existence of NPC classes has interesting implications for the economy of your setting.
The written rules for scaling encounters don't adequately address the complexities of additional players in the party. This article presents alternate rules for scaling encounters to accommodate additional players.
Minion, Mooks, or Extras. Whatever you call them, disposable enemies that fill out encounters are a welcome addition in many RPG systems, but have never officially made it into Pathfinder. This article takes lessons from 4e to adapt minion rules to Pathfinder.
Fantasy Flight's Edge of the Empire includes the "Obligation" mechanic, which establishes ongoing obligations for the player characters. These obligations have both social and mechanical implications for the game. This article adapts the Obligation mechanic for Pathfinder.
The relative power level of your player characters can heavily influence the play style of your game. By understanding and reigning in the options available to your players you can get a better handle on the players.