I'm with you there.... but then I really don't filled up my save games because it's not my play style to do so. My rotational saves might have more sims but it rarely even hits 150 sims.
The few times I've had a really populated save.. One I downloaded and a celebrity save that I just kept adding on too... I would have problems with lag or odd glitches when I actually stopped messing with the families and decided to play. I've since deleted or thinned those saves out.
I do like the freedom of being able to drop in restaurants, businesses or anything I want and not be concerned that I won't have a lot to put them on.