オブジェクト指向は iPhone アプリ開発で、どのように役立っているか

import UIKit

class ViewController: UIViewController {

    @IBOutlet var bilirubin:UISegmentedControl!
    @IBOutlet var albumin:UISegmentedControl!
    @IBOutlet var pt:UISegmentedControl!
    @IBOutlet var fukusui:UISegmentedControl!
    @IBOutlet var nosho:UISegmentedControl!
    @IBOutlet var childIndex:UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func selectorChanged(){
        let b = bilirubin.selectedSegmentIndex + 1
        let a = albumin.selectedSegmentIndex + 1
        let p = pt.selectedSegmentIndex + 1
        let f = fukusui.selectedSegmentIndex + 1
        let n = nosho.selectedSegmentIndex + 1
        let childPoint = b + a + p + f + n
        var childGrade = "A"
        switch childPoint {
        case 5 ... 6:
            childGrade = "A"
        case 7 ... 9:
            childGrade = "B"
        case 10 ... 15:
            childGrade = "C"
        default:
            break
        }
        childIndex.text = "Child \(childGrade)  \(childPoint)点"
    }
}