Not that much of one. I mean All in the Family and Barney Miller, in particular, were basically dramas that happened to use the sitcom format, mostly because it was the closest television gets to stage plays.
I mean so many of the great plays of all time are basically people in a room talking. There are even thrilling adaptations on film of dramas for the stage, some clearly dramas, some blurring the line between comedy and drama.
Look at Educating Rita, Doubt, Frost/Nixon, the works of Tennessee Williams, The Philadelphia Story, You Can't Take it With You, The Petrified Forest, Key Largo, Proof, Rope, the works of Anton Chekhov.
Hell, actual films like My Dinner with Andre are potent dramas without any plot.
There are no rules, except what works.