While I tend to heavyweight most of my 1x1s and do most of the plotting and NPC-ing, I like my partner to have equal input so we both enjoy the plot, and if they have a great idea, it can be incorporated. We also each have our "assigned" main characters, then share the NPC-ing of everyone else. Sometimes, it's just easier to switch off some of the heavier NPCs, especially if one partner has multiple MCs that need to interact with them while the other doesn't at the moment.

[b]Example:[/b] I have a 1x1 [i]Nightmare Before Christmas[/i] AU. My main characters are Lock, Shock, and Barrel, my partner's are some of their monster OCs to play off of them. Depending on the scene, we share characters like Jack, Sally, Dr. Finklestein, and the witches, since they're heavyweight NPCs that our main characters end up running into often, and then the rest of Halloween Town as in-general NPCs as needed. Sometimes it's just easier for my partner to take Jack so LSB can play off of him, or I'll take Jack and Sally because more of their monsters are in the scene, but LSB aren't, or if it's a big crowd scene, we'll [i]both[/i] play various Halloween Town citizens and switch off Jack as needed depending on what's easiest to keep the flow going. Just whatever needs to be done, we [i]both[/i] have the power to do it instead of relying on one person playing this one NPC all the time.