Cheaper goods, larger market, more things to market, age demographic balance, broader cultural influence (inasmuch as one believes this to be a good thing), increased chances for innovation.

All or some of this probably ties into what people mean by "economy", but I think it doesn't lend to any appreciation of the material difference that having more people thrown at a problem presents.

Taken to the extreme: a world void of other humans might be entertaining but would be a woefully inefficient place to learn about medicine or the cosmos. Which again presumes an audience who cares about any of that, but I wager that many do. Automation certainly replaces some people for some tasks, but we haven't escaped the need for humans yet.