Spring源码 If a @Configuration class gets proxied 如何理解？

Question

ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();
for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {
   AbstractBeanDefinition beanDef = entry.getValue();
   // If a @Configuration class gets proxied, always proxy the target class
 beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
   // Set enhanced subclass of the user-specified bean class
 Class<?> configClass = beanDef.getBeanClass();
   Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);
   if (configClass != enhancedClass) {
      if (logger.isTraceEnabled()) {
         logger.trace(String.format("Replacing bean definition '%s' existing class '%s' with " +
               "enhanced class '%s'", entry.getKey(), configClass.getName(), enhancedClass.getName()));
      }
      beanDef.setBeanClass(enhancedClass);
   }
}

请问上图中设置的哪个属性有什么意义，该如何理解？

延伸问题一：

延伸问题二：

这个配置有什么意义啊