A caveat to this study: the researchers were primarily looking at insect pollinator biodiversity. Planting a few native wildflowers in your garden will not suddenly cause unusual megafauna from the surrounding hinterlands to crowd onto your porch.
That being said, this study backs up Douglas Tallamy's optimistic vision of Homegrown National Park, which calls for people in communities of all sizes to dedicate some of their yard (or porch or balcony) to native plants. This creates a patchwork of microhabitats that can support more mobile insect life and other small beings, which is particularly crucial in areas where habitat fragmentation is severe. This patchwork can create migration corridors, at least for smaller, very mobile species, between larger areas of habitat that were previously cut off from each other.
It may not seem like much to have a few pots of native flowers on your tiny little balcony compared to someone who can rewild acres of land, but it makes more of a difference than you may realize. You may just be creating a place where a pollinating insect flying by can get some nectar, or lay her eggs. Moreover, by planting native species you're showing your neighbors these plants can be just as beautiful as non-native ornamentals, and they may follow suit.
In a time when habitat loss is the single biggest cause of species endangerment and extinction, every bit of native habitat restored makes a difference.