Get confused by the description of QFlags

Hi guys,

I'm confused by the document of QFlags. 

The document says that, because of C++ does not provide the type check for OR operation of enum type, So any enum value can be OR'd with any other enum value and passed on to a function that takes an int or uint.

But, even if I use QFlags, I can also OR two different enum types and pass it to a function which take int . 

// code placeholder
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include<QQmlEngine>
#include<QDebug>
class ClassA{
 public:
  enum Option{
    UTF8,
    GBK,
    GB2312
  };

};
class ClassB{
 public:
  enum Option{
    UTF8,
    GBK,
    GB2312
  };
  Q_DECLARE_FLAGS(Options, Option)
};
Q_DECLARE_OPERATORS_FOR_FLAGS(ClassB::Options)
void function(int option){

}
int main(int argc, char *argv[])
{
  ClassA::Option optionA = ClassA::GBK;
  ClassB::Options optionB = ClassB::GBK;
  function( ClassA::GBK | ClassB::GBK);
  function(optionA | optionB);
  return 0 ;
}

And the example code does not match the document, it use a function which does not take int , instead it take a QFlag. 

// code placeholder
label->setAlignment(Qt::AlignLeft | Qt::AlignTop);

But even if a function take a enum type, the compiler will also report error when you pass a var calculated by OR different enum types. I don't need to use QFlags.

So I want to know what is QFlags used for ?