This is a great drill to learn about timing and to teach swimmers to use body rotation to achieve optimal breathing position. Other areas that are promoted in this drill are a strong core position and the importance of the kick with regards to timing to create forward propulsion at the time of breathing.
Little pause at the back as you breathe - you don't want to be pushing straight down on the water with your lead hand to create your breathing position.
Rotation is key with timing
Kick timing to help with position as you breathe and to help maintain momentum,
Strong/ tall body position
Application to swimming
As you improve your UNCO drill then you can develop this with the first 6-8 strokes of each length UNCO drill and then swim the rest of the length. As you swim try to get the feel for the technique promoted by UNCO drill in your swimming.