If I am MUing, as in everyone is controlling one character in a scene, it needs to be live. I cannot do async in such a framework. I lose emotional connection to the scene and interest. After the second day, I lose complete interest and have already moved on.
If I am doing novella stuff, which I call collaborative writing and I haven’t done in decades because I’m picky and it has an even smaller population than MUs do, it HAS to be async. Someone (I’m not scrolling up to see who) was poo-poo-ing on this style, suggesting that such a framework focuses on the writing aspect at the expense of collaboration. That is incorrect. I would actually argue that MU*ing is much less collaborative as everyone in a scene tends to be looking out for number one with number one being their character. It’s a different mindset.
You don’t consider one character in the scene just yours. All of the characters are yours and all the other participants’ to work with to craft a good story. What you control is a portion of the scene not a character. It’s like improv with a lot of “Yes, and…” The other writers become partners and you have to work with what they give you and they in turn have to work with what you give them to craft an interesting fiction.
The focus is on having a good scene that, if an uninvolved person read, they would go “Damn, that’s a good bit of writing and a good story.” If this were in person, it would be less D&D and more story-game, like Microscope, City of Winter, and Fall of Magic, with something like a talking stick that gets passed around the table with the person having the stick getting to come with whatever they want but the other players have some form of veto power. Also there tends to be way more OOC discussion, figuring out where everyone wants the scene to go, what they want accomplished with which characters etc. Also also, it leads to people being more willing to have bad things happen to the characters, since there is less personal investment in a particular character. A character is just one of many that you use to write a story. I have argued that MU*s should adopt this style more but everyone tends to react to it like I’m suggesting we sacrifice infants to the Elder Gods, so whatever.