Some people simply find it interesting.
But it can also be an aid in studying plants and animals. If you want to look for more information on a certain plant, it sometimes help if you know what family and order it's in and what plants are related to it. There are two ways to explore the classification of plants that have been adopted as symbols. You can simply visit the U.S. Department of Agriculture's fantastic Plants Classification website and type in a common or scientific name. Or you can see the big picture with Geobop's Plant Taxonomy charts, which are linked to the USDA's website.