This is a method to deal with a concentrated position.
Essentially, you build a diversified portfolio around the concentrated asset so that it is no longer a concentration.
Obviously, this is kind of difficult for most investors, due to the definition of a concentration. If they have enough wealth to build a complete portfolio, then they don’t really have a concentration…
I think the more practical “real-life” version of this method is that you slowly sell out of the position over time to get to a diversified portfolio. So if you start out with most of your wealth in Exxon stock, selling some of it every year and using the proceeds to diversify. This can spread out the tax consequences but leaves you exposed to unsystematic risk.