Opens a new window where data can be plotted.
Since it is possible to have as much as 8 plots in a single window (this can be done from Plot->Plot Type/Routing/Test...), one can ask what the purpose is of adding a new window.
The answer is that the post-processing/plot settings in a window is independent on the other windows.
For example, you want to plot the frequency response smoothed and unsmoothed simultaneously. This cannot be done by selecting two frequency response plots in the same window like shown below, since the settings will be set equal.
In the picture below, we are using two windows. This makes it possible to have different plot settings (the lower window has a smoothed curve).
In other words, the settings are independent in each window, but they may be dependent when using several plots in the same window.
After you have selected Window->New Window…, you will be asked what post-processing setup you want to load in this new window as shown in the figure below.
If you click the button, the new window will contain the same settings as the plot window that was active when you selected Window->New Window….