Benefit for the plants i would say as far as we know it would be far fetched to claim it is. But what do we know? There are studies done that revealed that plants react and act too much more stimulus and seem to have higher intelligence than previously believed and known.
But we yet we didn't get to the bottom of it.
Benefit for the fish? IMHO and experience absolutely a big YES!! I played for a number of years with such light effects simulating cloudy skies. And schooling fish depending on the region they like to swim react to it rather positively. For example, under higher light, they rather are more cautious and stay in the mid-range or even closer to the substrate. In lower light levels they feel much safer to come closer to the surface. Hence floating plants are equally welcomed by the fish for the same reason, it dims the light and it provides shelter and a feeling of safety.
I went so far to not only create a dynamic light schedule, that's the beauty of DC voltage and PWM control.
I also created a dynamic flow pattern with a DC 12 volt water pump to control its speed in a schedule via PWM. And also this i observed as very positively received by the fish and it changes their behaviour according to the flow change. Avoid it or come to play in it...
Nature is a very dynamic environment were a lot of sudden changes take place fishes to have to endure. Since the fish has a big part of the stream to explore. Then it's not hard to imagine that partially recreating such a dynamic environment can only be received as a welcome. Not saying a fish is bored to death in a rather small static artificial environment... But I'm pretty convinced fish know what fun is and will have it if given to them.