Stina1701A ..I can understand the concern regarding memory etc thus the "run out of space" but the sim files must be different then in the past because in sims 3 you could save up to a reasonably long time but when it was getting "hefty" it would bog down and you would know it was time to wrap it up and start with something new. I would imagine however ...it is wise to decide how large your family should be and you can send some of your sims packing to keep your focus on the families you want..i am learning a lot from the folks that post in here.
I have already experienced a "surprise" and that was discovering that one of my single male sims really doesn't like the other single male sim i moved in to be a good friend...now that might be a ways off or maybe never because they really do not get along. But that is ok. Surprises was kinda what i wanted.