It's mostly considered the "classic way" of playing The Sims: Creating a single sim, let them level up in their careers, let them marry and eventually having kids. I never tried before some months ago when I created a single sim, not a family, and tried it out myself.
In TS4, I would become bored too quickly when I don't have a family or roomies household that I play parallel to the single sim - this isn't the case in TS3 - the game seems to be so rich in gameplay that I was never bored with the single sim I created - now he's married, I wouldn't have come this far with TS4 in ten years
Now I will try this with one or two other sims too!
Want some starter houses? Look up my gallery! Origin ID: Huiiie_07