Do you think is OK to keep Monarchy going in some countries? Is it useful?

I think it's best not to be too doctrinaire about this issue. "If it's not broken, don't fix it" is a good general rule. There are many countries where a constitutional monarchy is working quite well. Also, it has to be said, looking at countries in the middle east and parts of the Third World eg Africa that the monarchies are more stable, less prone to chaos and cruel dictatorships than the republics.