The outer regression (green straight lines in the chart) tracks the main trend. It save you from working out your own trend channels, BUT it does move with the price, so it is different from a static channel. You can use it as a template for drawing static channels though.
The inner regression (the curved lines) is a parabolic regression. It shows the shorter term trend within the outer trend. This helps traders to judge when it is right or wrong to take a position on the edge of the main regression, based on whether the inner regression is indicating an acceleration out of the channel, or is shaping to go with the main trend.
We find it works best if there is a clear trend. If the market is not trending, then there isn't much point using a trend analysis tool like this.
Like all indicators, it is not perfect, and you should never rely on one indicator in any situation.