One purpose of discriminant analysis is description--finding a way to separate and characterize the three species in terms of differences on the classifying variables. In the Iris data, Fisher saw that size matters--members of a certain species tend to have larger values for dimensional measurements on the individual samples such as petal length and width and sepal length and width. In addition, there was another pattern--members of a certain species that otherwise had small dimensional measurements on three of the indicators had relatively large sepal widths. Taking into account both of these patterns, one is able to classify irises with great accuracy as well as understand what characterizes exemplars of each species.
In descriptive discriminant analysis, you would report and focus on summary statistics within groups such as means, standard...