There are different versions of some of the planes. The ARF version requires you to glue the wing together at the center. When the ply wing joiner is properly-installed into its pocket, and the rib faces on the wing halves are glued together with NO gaps, the wing's plenty strong....the two halves and joiner provide plenty of support.

The RFT version has a slip-together wing that is not glued in the center. The two wing halves do not help support each other in any way. That's why there's a steel rod to provide support across the center.

One method is not superior to the other, they are just different because the structures of the wings are different.