Current forces fish to move and work.
In nature, they have to work to find food.
And nature is a huge place unless you are a desert pupfish or something vs our tanks.........

They need some exercise.........
Larger predators, discus even can benefit from a few hours a day(not all day etc).

The plant beds offer refuge also, since current is highly reduced there.
Giving fish some places to swim against current is nice for them, you do not/should not place them in a tank where they cannot get away from high current though.

Even coral tanks need some patterns of calm, not continuous current.



Regards,
Tom Barr