Plugin development: site settings "enabled" checkbox not working

I face similar issue.

enabled_site_setting :myplugin_enabled
after_initialize do
  ::Topic.class_eval do
    after_commit do
      #myplugin code
    end
end

No matter if myplugin_enabled is true/false, myplugin code is executed. I don’t see any use for enabled_site_setting either. Can anyone explain what exactly it is? How can I enable/disable myplugin code based on myplugin_enabled value?