The brilliance? It pays off arcs.
In my efforts to keep my fan-fiction romances going, I began to add in characters: a Victorian guy who was kidnapped by Loki, placed in status by Thor, and returned to Earth with Jack. How does he cope? A grumpy citizen from Pelops, who is greatly tired of all the happy people. A gruff, embittered FBI agent encountered during the run-in with Set/Seth.
Whenever I felt that one relationship had reached completion, I brought in a new one.
This is not quite the same thing as throwing in extra characters. Seven-of-Nine worked but Ro Laren didn't much. But since my focus is romance, it worked for me!
And I realized that many romance manga series--yaoi and shojo--do the same thing. The main couple isn't constantly put through the wringer. Instead, other couples enter the picture, get their own story, and then step back for yet another couple to have its time in the sun.
As a writing solution, keeping the core stable while altering the "big bad" or the current relationship trouble is quite intelligent. That SG-1 producers/writers did it with action/adventure is impressive, especially since they found (more or less) the best line between drawing the viewer in with the most important element (the team) while changing out the bigger plot elements.It also explains why something like Quantum Leap doesn't fall to pieces: as long as Sam & Al are our guides...