Previously, I'd talked about how the DM+1 style brings changes in the distribution of attention, necessitates a roundabout approach to collaboration, and alters pacing. This time, I want to continue looking at the non-mechanical side of things by talking about the scope of the game. Similar to what I had said about pacing matters, this isn't something exclusive to DM+1 play, but I think it becomes more important when there's only a single player.
To touch back on what I'd said before, DM+1 play tends to be closer to the implied experience when people use analogies to works in other media to describe D&D. In fact, even though I'd said the Lord of the Rings series was an example of a work that features a protagonist team, consider the case of Frodo Baggins. He starts out as one of the gang, setting out on a great journey, but that's not quite true. He's the special one, the Ring-bearer, the one who's bound to gain the lion's share of either credit or blame for how the quest to destroy the One Ring goes. The purpose of the fellowship is to support Frodo, since he's allegedly the only one among their number that can bear the Ring for so long without becoming corrupted. Sure, Aragon is the king in exile returning to reclaim his throne, but Gondor is worthless if Frodo fails. Gandalf is basically an angel, but even he can't stand against Sauron. The rest of the fellowship's members are all even less significant in the greater view; they have their parts to play, yes, and each proves necessary, but ultimately, none are as important as Frodo.
Unfortunately, while that's a good story for a novel series, that'd likely be an annoying narrative to actually play out in a D&D game for anyone aside from the person playing Frodo, especially if they didn't agree to it beforehand. Even Frodo's player would probably get tired of deflecting accusations of favoritism and sexual conspiracy theories.
What if we look at something more equitable, then? How about the Wheel of Time? Rand holds the most crowns, sure, but Mat, Perrin, Egwene, Elaine, and more end up gaining titles over the course of the series. Even accepting that that was all a means to an end of defeating the Dark One, isn't it just a fine little series of coincidences that they all got together? Don't we all love stories where everyone in the team ends up inheriting a state, leading a pan-national tribe, etc.?
Well, no. I tend to find such narratives contrived and unfulfilling, but maybe that's just me.
The point I'm getting at is that D&D narratives that involve a team of PCs fulfilling epic destinies or becoming heads of states tend to have major problems in practice. However, if there's only a single PC, it becomes far less of an issue for them to play the chosen ring-bearer or the crusading princess because there are no other PCs for them to overshadow or leave out of the VIP clique. Consider everything that Conan accomplished by the start of Hour of the Dragon. A PC doing even half of that as part of a team would be a Mary Sue gloryhound, but a solo PC doing it would be a personal legend.
Thus, if you're running a DM+1 campaign, feel free to aim big. The PCs should always be influential within the narrative, of course (otherwise, write a novel or screenplay instead of using other people as your marionettes), but DM+1 play is a good opportunity for them to be influential within the setting itself. Maybe don't start big if you don't have any checks against PC mortality, but assuming the player would be into it, there's no reason why that street urchin PC standing up against the corrupt tyranny of the establishment can't turn out to be the lost heir of the rightful ruler, why the unremarkable bystander PC caught up in a swirl of fantastic events can't turn out to be some hero of prophecy, or why the vagrant who barely survived being run down and imprisoned can't make a deal with a devil to enact some genocidal revenge. Not only would it be a chance to do something that'd be more perilous with a larger group, but having that grander scale can also help to maintain excitement and interest in lieu of the players being able to do that amongst each other.
That's all arguing in favor of increasing the narrative scope. However, DM+1 play also facilitates (and demands, I'd argue) zooming in more on the fine details, too.
When playing with a larger group, there's usually considerable pressure to keep things moving. Even with a small group of, say, three players plus the GM, assuming an even split of spotlight time, each player spends roughly twice as much time witnessing the others play as they do playing actively. It's not actually that bad in practice because witnessing others play is also fun and that passive time can be spent thinking about what to do next, but it's usually good practice for the GM to keep shifting the spotlight around to keep everyone engaged. That means the depth of play for any individual player is usually less than what it could be without external pressures.
When there's only one player, though, there's no need to make that compromise. The player (and the GM) can go further into the details of the PC's interactions, reactions, emotions, etc. In other words, while DM+1 play does necessarily reduce the fellowship aesthetic, it can make up for it with increases in the fantasy, discovery, and expression aesthetics by increasing the attention on roleplay depth. If the player wants to manage the logistic details of a rebellion, pursue a courtly romance, or plot out the fine details of their onion of conspiracies, they can do that without feeling like it's taking playing time away from someone else. If the player wants to explore every room of a dungeon in minute details, see how cleverly they can outmaneuver a political rival in a public forum, or wring out every drop of information from a prisoner, they can do that without anyone else growing impatient.
In the previous post, I'd mentioned that scope could help to offset the greater speed of play. This is where you can see that happening.
To be clear, I'm not advocating for drowning DM+1 players in minutiae. The player's interest and engagement, together with the GM's, should be a major part of deciding what gets detailed to death and what gets glossed over. When there is something that they latch onto, though, take your time in exploring it, because that depth is a key part of what allows for experiences in DM+1 games that tend to be sacrificed when playing with a larger group.
To me, this variety in the scope of play is one of the best parts of playing DM+1 games. While there are obviously certain narratives that don't work in DM+1 play without extra effort (such as anything involving intra-party intrigue or tensions), I think the additional high-level scope that becomes practical and the increase in roleplay depth more than make up for that.
Let the PC be important within the setting, and let the player enjoy playing every bit of that character that they're interested in. Freed from worries about one PC overshadowing the others or one player hogging the spotlight, you might be surprised at just how much more can be done.