Edge control is often the key to efficient painting. As you've seen in Advanced Masking pt 1, nesting masks adds a high level of flexibility to the painting process. This video will continue the idea of nesting masks by exploring complex selections. Even if these ideas may seem abstract at first, they are worth learning. In my experience, once you begin to utilize methods like these you're able to approach Photoshop from an entirely different angle --- and will find yourself problem solving in a whole new way.
If you want to experiment with the PSD file from the lesson, here is the robot for download.