Worldbuilding: How would you build a world if the project lasted 10 years?

Practically everyone with an interest in worldbuilding has tried it, but only a select few consider it a life-long passion. Perhaps only 1/10 of those people really know what they’re doing. Professional worldbuilders have a deadline they need to meet, but how would they build a world if they had more time? Is there a difference between professional worldbuilding and amateur worldbuilding, and if so, what is it?