Flowers lead to seeds - to replant your garden 8. Flowers taste good. Flowers like chamomile, borage and foxgloves appear to make the plants they grow with more vigorous - see Companion Planting and Flowers 10. Most flowers have 'cottage kitchen' uses - you can make wines with them or make calendula ointment if you cut yourself in the garden. This meant that not only did they select for beautiful forms of useful plants - they also discovered uses for particularly lovely flowers like roses.
Flowers can help weed control.
Marigolds repel couch grass, dahlias will stop grass intruding in your garden, a thick crop of poppies will help clean up weeds, cornflowers stop some weed seeds germinating, thickly sown sunflowers will stunt weeds and choke them out.