Aql is basically using your mental capacity to choose right from wrong. To prepare for the Akhira and worship Allah properly. A person can have a high IQ, but they can be evil and corrupt. So both intelligence and intellect are similar in that they use mental efforts and calculations, but the intellect allows you to do that which is right.
If one’s intellect increases, they:
Get closer to Allah
The worship Him in a more complete way
They sin less
They help people more
They prepare for the hereafter more