This is a very cool concept that I’ve admittedly only ever really employed once, and it wasn’t really in regards to inactive players, it was just to handle a very large encounter in a Heavy Gear game. It actually ended up being one of our more memorable sessions, actually, as the players ran their adversaries: a southern (French-speaking) unit that they were battling in a stairway. Things got a bit silly, but even to this day we’ll jokingly shout things like “Jean-Marc! Non!!!”
I’ve never really used ‘Jamming’ for any serious roleplaying encounters that I can recall, but I can see how it could be very useful in keeping things livened up for players who’s characters aren’t present in a scene.
There are a few obvious approaches to resolving this situation. The DM can run scenes with each group of heroes in turn, giving the inactive players an opportunity to fetch a snack or use the lavatory, or the DM could also divide the various PC errands into smaller scenes, switching between groups more frequently so that periods of “down time” are shorter.
A third, and more entertaining, option was briefly outlined in the recently released fourth edition Dungeon Master’s Guide 2, but discussed at length in the second edition, out-of-print Creative Campaigning supplement, published by TSR Hobbies in 1993. The authors of that supplement called the option “jamming,” and it greatly reduces player inactivity when only some heroes are in the spotlight.
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