This is a drill to practice good hits at medium range from different angles while using cover.
The point here is to properly use cover of an odd configuration to engage a target several times while never emerging from the same place twice. Four shots from four different positions forces you to learn to use your body to provide a stable platform based on what the cover requires of you…all while maintaining good accuracy on a small-ish target (here 8″) at medium range (in this case, 23 yards).
You’ll notice that I finish with covered sul position. This is so that I can scan my area for more threats while not looking like a deadly threat to friendlies in the vicinity. Most folks won’t even notice that there’s a gun in my hand (have a care not to unnecessarily frighten folks when you’re doing good).