What really kicked this off was me looking through Holmes Dungeons & Dragons last night & then reading about The Ghayat-al-Hakim or Picatrix posted by RpgPundit.
The Picatrix could the lynch pin to an entire old school campaign because its a huge part of Arabic occult history. Wiki has a solid entry on it but the gist of it goes something like this;
" Picatrix is the name used today, for a 400-page book of magic and astrology originally written in Arabic under the title غاية الحكيم Ghāyat al-Ḥakīm, which most scholars assume was originally written in the middle of the 11th century, though an argument for composition in the first half of the 10th century has been made. The Arabic title translates as The Aim of the Sage or The Goal of The Wise."
When you begin to look into the monsters, treasures, & other adventure elements of the old school on thing becomes apparent, the PC's are the heroes. They're deeds are going to change the history of the campaign setting or their bones will molder & decay for others to find. This isn't the cosmicism of HP Lovecraft but very nature of Dungeons & Dragons style dungeon mastering & adventure playing that happens to line up with this style of belief. So let's turn the introductory aspect of Holmes on its pulpy ear.
Many times though out Dungeons & Dragons the fact is that Earth, Greyhawk, Avalon, etc. are all cosmic back water settings in the wars,struggles,battles of the greater occult & planar universe. This means that the deities, monsters, etc. are all chess pieces in the larger context of the war between the forces of the universe. There isn't simply one front in this meta war but many.
This was something that was mirrored in Original Dungeons & Dragons's Eldritch Wizardry & Gods, Demi Gods, & Heroes not to mention Paul Anderson's Three Hearts & Three Lions which gets quoted so often about in certain OSR circles. So were the writers & designers of Dungeons & Dragons trying to promote the occult and lead our children to the infernal?
TSR 2005 Dungeons & Dragons D&D Original Supplement III 3 Eldritch Wizardry 8th
Umm no they were trying to use the trappings & ideas of mythology to create a viable set of tools for old school play so you could design campaign setting of your own. You can even see this evidenced in this video review of Holmes where the commentator brings up the point that Holmes was a transitional set of rules until Advanced Dungeons & Dragons hit the market.
This means that the mythology of 'Chaos vs Law' has always been a part of the equation of Dungeons & Dragons which in turn plays its own part in the mythologies of the cosmicism of HP Lovecraft, Clark Ashton Smith & the Lovecraft circle of writers. Its very operatic in its own terms. Now we come back to the Picatrix which according to Eugenio Garin," Astrology in the Renaissance: The Zodiac of Life" , Routledge, 1983, p. 49"The work's point of departure is the unity of reality divided into symmetrical and corresponding degrees, planes or worlds: a reality stretched between two poles: the original One, God the source of all existence, and man, the microcosm, who, with his science (scientia) brings the dispersion back to its origin, identifying and using their correspondences"
This is exactly the sort of thing that we see in Gods, Demi Gods, & Heroes by James Ward & Robert Kuntz. It taps into the types of influences that we've seen in popular comic books for years especially those of Jack Kirby in both his Marvel & classic DC days.
On the more contemporary side of the OSR, Lamentations of the Flame Princess by James Raggi IV, Dark Albion By RPGPundit, & even The Midderlands Additions From MonkeyBlood Design all take advantage of their settings as planar back waters. There are far worse monsters, gods, and things out in the greater universe that can wreck the PC's.
But that's always been my point before the PC's are the heroes & in terms of adventures regardless of level their struggles define the frame work of the campaign. They may raise the bar from back water to stage presence. For Astonishing Swordsmen & Sorcerers of Hyperborea second edition or any of the other retroclone systems that might not be a good thing. For many science fantasy authors the age of heroes has passed but the PC's have a chance to bring it back. Der Ring des Nibelungen is a fine example of the consequences of interfering in the workings of the gods & its repercussions for a campaign setting.
Recently Oakes Spalding on the Save Vs Wands blog did a quite interesting & expansive look into demons in Demons in Holmes,the Monster Manual and the Players Handbook. My conclusion is that demons are a fulcrum tool to kick a campaign into a higher gear or bring the PC's onto the larger stage of adventure. This is where I think that a campaign world goes from back water to player in the cosmic scheme of things. The PC's actions, struggles, deaths, and triumphs are what make the mythology & difference in the campaign.