Creating the Non-player Character

When considering the ability stats of non-player characters, we would do well to remember that NPCs are not participants in the campaign.  They are a part of the setting, there to act as aids and obstacles, a means of delivering exposition or to impose an authority the players dare not confront as yet.  NPCs may be stock figures in the campaign when they're not needed to fuel the adventure's momentum; or they can be central figures that the players will know and interact with for a long time.  Therefore, the NPC's abilities should be based on what they're bringing to the campaign, and not necessarily upon a die roll.

If the NPC is of not importance, then we need not roll the die at all ... but if the NPC is an heroic fighter, then assigning a high strength that fits the campaign's needs.  Do not roll.  There is no "game" in the creation of an NPC.  Some are window dressing, some are key tools in structuring the campaign's feel, or atmosphere.  Obviously, a DM needs to give careful thought to how strong or intelligent or high level an NPC is; but this thinking process is not improved by handing the problem over to a non-thinking die roll.

Now and then, particularly with associates of the players, where we want to be fair in giving them support troops in the campaign, it is well that we roll 3d6 for their stats, or even a bit better.  Such NPCs, embroiled in the fight side-by-side with the players, can be said to "play the game" in an ersatz manner.  However, apart from such conditions, there are really few times when the DM should be concerned with rolling.  This doesn't mean every powerful and competent NPC has an 18 wisdom or dexterity!  But it does mean a DM shouldn't be wasting their time rolling up long strings of secondary game persons who can be assigned abilities on the spot, saving preparation time by recognizing that exactness is not always a virtue.