Atlatl Jones
Explorer
This is exactly my problem with it.Knowledge skills - it actually makes a difference whether you just know something about arcane lore or religion. It makes a difference if you know something about the undead creatures or the dragon...
But the difference between Perform (Lute) and Perform (Drums) is minuscule in game effect.
Any skill could be divided into multiple sub-skills. Sneak used to be divided into Hide and Move Silently, and could logically be divided into various types of sneaking, like Sneak (forest) or Sneak (urban shadowing). As a result, the decision whether or not to divide a skill into multiple sub-skills should be based on the in-game effect of the division.
Knowledge skills are useful. Ranks in Knowledge (the planes) give an entirely different functionality from ranks in Knowledge (nobility) or Knowledge (arcana). But Perform (wind instruments) and Perform (stringed instruments) have virtually identical effects in play. A GM would have to try really really hard to make a meaningful in-game difference between those skills, and in the end it would probably feel like something that was created purely to justify taking those different skills, rather than something that was necessary for story reasons.