It would be more efficient with ems, but we can’t make ems yet. Technically we could already colonize space; it’s expensive, but still, it’s closer. Think about why old-world people colonized the Americas (and everything else they could, anyway). The basic cause was space and resources. Of course, with current tech we can extract much more value and support a much larger population in Europe than we could at the time. But even if they anticipated that, it still wouldn’t have made sense to wait.

Even without total utilitarianism, increasing the population may be desirable as long as average quality of life isn't lowered. For instance, increasing the amount of R&D can make progress faster, which can benefit everyone. Of course one can also think of dangers and problems that scale with population size, so it's not a trivial question.