How do you use setting material? Is canon important to you?
I was thinking about this thread some more after my last post.
During the long era of 2nd Edition D&D, I used to get stuck on the wider body of Realmslore (aka Canon) when running D&D campaigns.
I knew where I wanted to set my campaigns and what I wanted to do with them, but I also felt like I was obligated to make the campaign fit into the ongoing story of the Realms. This entailed spending a lot of time checking to see if my plans would interfere with major events and ongoing plots unfolding in any of the dozens of novels and sourcebooks being released, which also entailed buying those products and reading them cover to cover.
That's when DMing felt more like a job than a hobby or leisure activity, and boy oh boy would that time have been better spent on practical campaign prep (building dungeons, creating encounters, etc.).
I used to worry about being called out at the gaming table for getting a fact or NPC or event wrong. My gaming friends did it to each other sometimes, and they were as much into the setting as I was so I figured accuracy mattered.
A big help with this came in the form of time: I got older, I moved out, and I found new gaming friends (read: older gaming friends) that had a wider experience with non-D&D game systems and so were not as focused on the Realms as I was.
They helped me to realize that a player's enthusiasm for a campaign world (regardless of system) isn't always about obsession with accuracy, it's about immersion. Sometimes players want that special vibe that comes with playing D&D in a fantasy world that you've explored through novels or computer games: A place where a lone drow ranger walks the surface world and kicks butt and there's a chance you might run into him is fun to explore.
And it's
exciting to send a character down the well in the center of the Yawning Portal and face the dangers of Undermountain for the first time, just like it's a little terrifying to realize your DM is starting his or her new D&D campaign in the ruins of Myth Drannor (not a place where low level PCs last long).
Usually a player's enthusiasm is centered on their new character. It's all about their back story, race, class, combos, and tactics built around the characters the other players plan on running.
What I realized was that interest in a campaign world is another form of enthusiasm, and I needed to capitalize on that, not worry about it.
So I try to figure out what my players know about the Realms so that I can avoid breaking their immersion during play--which I guess is another way of saying "caring about Canon" means the same thing as saying "caring about your players".
If I don't know more than a player does about a certain topic of Realmslore then I'll probably shy away from whatever part of the Realms they like (unless or until I decide to bone up on that area lore-wise). If I know more than they do then I'll seriously consider focusing on their area of knowledge in my campaign plotting because that's a surefire way to keep them coming back for more.
If I know more than all or most of the players (which is usually the case) then I have tremendous leeway to do what most people do: use the campaign world as a source of NPCs, encounter locations, and so on. And that's really what the Realms is supposed to be: an enormous resource of useful information that is meant to be borrowed from to whatever degree a DM desires in order to help him or her build a campaign that is enjoyable and believable, and a fun experience for everyone at the gaming table.
In other words: take whatever Canon Realmslore you need and ignore the rest.
Therefore, regardless of the balance of Canon Realmslore knowledge I find among my players, I know that keeping the campaign world as presented during play at the gaming table as consistent as possible with itself is my most important job.
Keeping my campaign consistent with what's published by TSR/WotC for that campaign world is not a primary concern.