I've been mulling over a recent experience in a Pulp Cthulhu 7E game where the players each got to run 2 characters. I think some of the rationale was it was a scenario designed for a lot of players but we were a small group. It was also potentially a very deadly scenario, so maybe multiple PCs left some wiggle room for death without taking a player out of the mix. The key thing, though, is that it meant that I was trying to juggle more than one PC, and it was an experience that made me think about another game I've been interested in recently: Dungeon Crawl Classics (as well as Mutant Crawl Classics) and their funnel mechanic.
Here's the thing: I really disliked juggling 2 PCs. I realize this has to do with my play style as a player, because as a GM I of course must juggle lots of NPCs. As a GM the process is simple, because the NPCs are not PCs, they have their moment/turn of events and are tied to the plotline....as much as I choose to ham it up, NPCs are still there to act as foils for the PCs to play off of, letting the story move forward. That is a distinctly different experience from what I want as a player.
As a player I imagine there are a few types of people out there who engage with their character in different ways. Ways I have seen include:
Speaking of your PC in the third-person tense ("James tries to open the door.") like you are an author narrating a protagonist's actions. A lot of new players who haven't role played before start here then work out their comfort zone over time.
Speaking in first-person, but playing, in essence, yourself (you are invested in actions, but not necessarily immersion; dialogue will sound like this: "I talk to the demon to see what it says it's name is."). Players who settle here tend to be playing a role, yes, but are not really role-playing in the conventional sense.
Speaking in first-person, but playing a character (you may change your vocal tone, accent, or even go a bit out there: "If you, sir, are possessed by a demon, then how might I address you?"). A majority of long term gamers tend to nestle here after a while, and most tend to have a range of around 2-4 "types" that they favor, sometimes with varying personalities and other times with varying playstyles to match.
Speaking in first-person in charicature; these are the players who either are amazingly good at it and bring some genuine thespianism to the table, or they are an earsore and we all suffer, but they are key in always being exaggerated in their personality and voice, and indeed their main satisfaction may be less in following the story of their PC than in the representation of it. This kind of player is actually not that common in my experience.
Anyway.....I have a theory that the multiple PC methodology does not mesh well with all but the first type mentioned above. It creates a disruption when you are a focused player who likes to figure out a character, but must then "jump tracks" every turn to figure out a different chaarcter. In the recent games I found myself resorting to third-person narrative for my secondary PC just because it was the only way to keep things sane in my head.
When I have run my own games, if a secondary character becomes necessary I have always identified them as NPCs who act as henchmen under mechanical control of the player, to which I would then lend the personality or decision making if needed (it is not too common the player is good at this, unless the NPC/secondary character is something easy to manage like an animal companion). This has worked well; I've run games where there were 3 PCs but each had 2-20 henchmen, whom they could direct and control, without worrying about the personalities.
As a result, this got me to thinking about the funnel crawl and its design intent in Dungeon Crawl Classics. The theory is that putting a massive group of zero level PCs who are definitely fodder for the module will let players bond with the survivors. It's an interesting idea, and may work, but does require that the initial game be, in essence, about "no one" at first, and that the disconnect of the player to a mass of PCs will in theory subside once one or two of them are all that is left. I want to see how this works in play, but worry that it would be less exciting than it sounds.
I do know one thing out of all this, though: aside from not liking controlling two or more PCs equally as a player (in Call of Cthulhu, at least!) I also don't much care for the Pulp Cthulhu rules. Too unCthulhuish! But that is another blog post for another day.