One way to use the logarithmic regression curves is to find the "Fair value" of bitcoin. The fair value is the natural regression of the price of an asset, stock, or crypto coin. It's hard to determine the exact Fair value of Bitcoin, but it is possible to use the lower levels of the Rainbow chart as some bounds.
As you can see in the chart, Bitcoin is currently trading in the lower bounds of the Rainbow chart, and one could argue it's currently in the "Fair value" price range.