Intelligence certainly has a practical threshold. If you have no intelligence at all you cannot thrive in a world of computers, pens, clothing, dishwashers... On the other hand, technology has allowed some areas to lower their intelligence thresholds. People who have severe mental disabilities can function in relatively normal lifestyles.

I'm not sure what you mean by "relatively normal". In countries like the UK and USA, about 20% of the adult population are said to be functionally illiterate. In a world where a normal lifestyle is rapidly coming to include using the internet, where applying for entry-level jobs can only be done online, these people are going to have major difficulties coping. This may well be a significant social issue in coming decades.