The MasterController Base Mod "provides functionality to manage the population of your town".
If I typed up a list of what MasterController does, I'd make a huge wall of post. So, we're lucky that twallan provides a handy
Interactions List to get you started. Since some of it might be a bit difficult to understand (Total Annihilation, for instance), here are some details about it.
MC provides a "Total Annihilation" option. What this does this mean? It completely and utterly deletes a Sim. It's as if the Sim never existed. For instance, in my Forumna Legacy, the 2nd Generation Spare, Teresa, was a vampire, and I sent her to Boarding School. Twallan's Overwatch Mod recovered her, and I had no idea if any repercussions would come about. So, instead of using TestingCheats' "delete sim" option, I used Total Annihilation. As far as the game is concerned, Teresa never existed.
I can't see many more options that I can explain (as in, aren't self-explanatory, and I don't know exactly what they do).