All the time. Most of my Sim couples don't even get married, just stay partners (or not, haha). I'm just not that into the child rearing concept or nuclear families. I like my Sims to have romance, adventure, drama, and make mistakes without being chained to offspring. I've even played where a single mother brought her unplanned child to the orphanage that I set up. I've never really felt the desire to have children in real life and I guess that carries over to the way I play the Sims. Many of my friends don't either. I think it's a lifestyle concept that's more common now in the modern era since women have been able to take control of their lives and have careers or be single without judgement. We've come a long way. :)
But I do like to create many Sims and colonize my worlds so I actually have a variety of households. Although I think the majority of them are single, childless, and/or dating. The ratio might change if we do get more personality and attraction adjustments or a romance pack. It's hard to hook Sims up with someone special when they all behave the same way.
