Light Loss Through Aquarium Sides

I was pondering if there is any benefit to covering the two sides of an aquarium to prevent light from escaping. In this scenario the back would be already covered and the front left open. I met a guy that allowed his coraline to grow on the sides and said it trapped more light inside thereby creating less overall shading. This he believed helped coral growth.
Obviously there would be some downsides, but still curious. Is there any truth to this? Wondering if anyone has any imput or experiences on the subject?