I’m currently running a game that USED to be a west marches game, we had 2 gms and 13 people total in a newly-discovered continent; now we’re down to just me and 6 players (plus guests every now and then). Since there’s a limited number of players now, everyone doubles up and chooses characters on a whim depending on where we’re going and who’s available. It’s basically come down to an ensemble cast, but it worked about the same before this.

A good benefit to dynamic parties is that the characters can have lives, motivations, goals, schemes, plots outside of the adventure party. It’s incredibly helpful for immersion. Your character just had a harrowing event? They can retire for a few weeks. Your character’s boring you? They’re needed by the mercenary captain for a few sessions. Your character wants to make a power grab on this Trading Company? Sure, why not. Characters can just disappear and achieve their own machinations outside of the game and basically become each other’s antagonists. There’s less story work required on my end since players basically create their own storylines. No longer must the party follow the Paladin to the bathroom because that’s where the party is going and it’s the paladin’s time right now and she really needs to shine her armor. If it’s not relevant to your character, you don’t need to be there.

The greater benefit is that all characters can be turned up to 12, since they’re popped in less often. Everyone has a few characters they’d *love* to play but can’t because there’s no way they’ll mesh well with X or they’re really only useful for Y and this campaign does Y Z and W. West Marches gives you a lot of leeway there.

It’s the benefits of a one shot with the continuity of a campaign, and a story with many moving pieces. And I need to do so much less of that story work than a normal campaign.