My guess is that it is used for lifting. Notice the two large threaded pieces. They look like they go into the holes on the top of the plinth. There might be two bars so that four people can lift it up into place. Then there are two more threaded pieces of smaller diameter for the platter. It looks like one guy in the photo is unscrewing the threaded piece from the platter.
That bar, and probably a second one, might also be used for securing the plinth and platter in a large wooden crate for shipping, but that too is just a guess. I'm sure David could elaborate.