Since schools and organizations that use the Chang-hon pattern set have many variations of the movements and how they are performed, it is difficult to interpret their intention of a movement. Your instructor should have more insight as to the school's interpretation of movements.
The movement in question a slow pressing block to the side using arc hands. As to its practical application, there is none. In a self-defense situation, one would never use a slow block since it would not be effective. Although, it may be used as a posture to show the attacker you are prepared and determined to defend.
Patterns are supposedly imaginary fights against multiple opponents. Therefore, sometimes blocks and attacks are performed toward different directions. This means that, while a sequence of movements may not seem rational when used against one opponent, the movements make sense when used against multiple opponents. Also, patterns have little practical application anyway.