Unfortunately Settings (Qt.labs.settings) cannot be used inside the component.
Real problems happen when you try to use Settings inside the qml document which is instantiated inside Component. Take a look at small example:

import QtQuick 2.7
import QtQuick.Controls 2.0
import Qt.labs.settings 1.0

ApplicationWindow {
  visible: true

  StackView {
    id: stackView
    anchors.fill: parent
    initialItem: thePage
  }

  Component {
    id: thePage
    Page {
      Settings {
        id: settings
        property int theNumber: -1
      }
      Component.onDestruction: {
        settings.theNumber = 42
        console.log("onDestruction")
      }
    }
  }
}

Configuration file will never contain "42" as "theNumber" value, it is always "-1". The "onDestruction" handler is called, but settings are not saved by some reason. If you remove configuration file while program is running, this configuration file is not recreated when program finishes.

Obviously, moving Settings outside the Component fixes the problem. But in real use-case the Component is far away from the main.qml files and it would be nice to declare its own settings close to the implementation.