@Cerulean0987
Well, you can control it to a certain extent.
If you are say in the Scientist career, the game will require a pool of I think six sims as coworkers for the job. When you go to work, it will pick a random 4 from the pool of 6 to accompany you on that day. If you only have say 2 others already in the career, it will create new sims to fill the other 4 positions. You can stop this by playing various townie sims briefly and having them join the career. If you have 6 sims in the career, the game won't generate any new ones. At least until one quits, retires, or dies.
But there are other jobs that will get auto-generated regardless, like bartenders, food vendors, DJ's...etc. I'm not sure how that works, but I have seen some of those positions filled by my own townies and not auto-generated ones. Some jobs like the DJs and acting gig jobs like Director/Producer always have generated sims.
There are some mods that can stop it, but those are rare. NPCC was good, but the current versions are always behind a pay wall for years at a time, and the free versions are very old and buggy. I always boycott them.
ThePsycho
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