If a plant has any use or perfoms a useful function within it's environment, it is practical. Since that definition includes almost every plant in existence, it's clear that it's really more of a shift in approach to working with plants: It is our conscious and intentional use of a plant for a purpose which makes a plant a 'practical plant', not an inherent property of the plant itself.
Cultivating plants based not just on their crop uses but also their functions and properties is fundamental to many systems of agriculture. Embraced in modernity by permaculture, bio-dynamism, companion planters, and organic gardeners, such an approach is as ancient as agriculture itself. It is nothing more than an understanding that working within nature and an exploration of the needs and outputs of plants is key to successful sustainable agriculture.