Circle-based crochet items are a great way to build a project of multiple radial symmetries around a central point.
They are wonderful for covering a portion of an area without obscuring the entire surface. For example, as a blanket, they highlight and counterpoint the bedspread underneath, or in the center of a near-square room, to let the young-one have a central point to focus and play on. The really attractive feature is that they break up the lines of an otherwise simple stitch, and allow you to make an interesting project without having to learn a whole slew of new stitches.
Rainbow Ripple Baby Blanket Free Crochet Pattern