Donna Levin
It is always satisfying for us as readers to see subplots that intersect with main plots; it appeals to our wish to see life itself makes sense. By “intersect,” I mean that the same characters apper in both the plot and subplots. It’s sort of like the way Mr. Drucker was in both “Green Acres” and “Petticoat Junction.”
From an interview with Donna Levin, 1994 Novel & Short Story Writer's Market.