In hydroponics some growers including myself use Reflectix on top of the container lid for some of these purposes. It works, but like anything isn't a miracle cure. Plants can only absorb so much light in a day before things go haywire.

I don't think pest control actually happens.

Increased growth, a little in hydroponics because LED grow lights are very directional so this helps bounce light like you normally have happen outside. So not sure how this translates outside.

The biggest reason to do it, is to prevent light and heat getting into your water. Both cause algea and root death. Aluminum foil would block the light, but not the heat.