At least the issue with that years ago was when minecraft would have an update that introduced some new generated resource where you would have to get to the edge of the map to generate some to use. Most servers restart periodically to get fresh resources near spawn, not only for new resources that might have come out in recent updates, but just because the area has been completely harvested by past players like some scarred piece of land and you need to start venturing out far to find trees or ore.