This is true on so many levels. Not only can you learn a lot about the ‘lane changer’, you can also learn about multiple others (even those farther ahead) by how they respond to the ‘lane changer’.
Do they unnecessarily slow? Or, if slowing is necessary, do they do it wisely? Are they caught off guard? Do they take advantage of the newly opened space? Are they looking ahead and paying attention? Do they use their lane to help provide more room to maneuver and to allow others to better see, accelerate or change lanes? (Most of these are ‘reading traffic’ techniques that we’ve already covered.)
Indeed, a single lane change is an opportunity to learn about multiple drivers in just a few seconds. Information that you can use to better predict their actions and time yours.