When using an incognito window, it is considered a new browser and there will not be any existing cookies. As such, we remove any unknown variables from the existing cookie such as previous visits, submissions, or similar.
This then allows us to accurately test whether or not a form is behaving as expected for new visitors, or if the unexpected behavior was a result of a prior form submission/visitor action.
For example, using new incognito windows will allow us to test how pop-up forms look and behave on your live website multiple times. Another example would be using incognito windows to test what a form with progressive fields would look like to a completely new visitor.