I always recommend adding a statue or some kind of sculpted object in a garden, for the following reasons:
BALANCE: A well designed garden contains balance of all its elements. Visual weight, textural contrast, layout. And too, the balance of hard and soft, natural and manufactured.
An elegant bit of sculpture gracefully introduces the manufactured element. It also gives the eye a place to rest amongst the multiple textures and colors of the plants.
DEPTH: Hedges and large shrubs stand their ground staunchly. The eye quickly dismisses them as a solid mass, a mere divider of a flat plane. But imagine, as you walk past the tall hedge, a gleam of white marble, and suddenly the block becomes a shell, and space curves.
SURPRISE: My childhood memories of gardens feel magical, because they are about surprise. A small tortoise under a bush laying eggs. An unexpected red bridge in a Chinese garden. As adults in a stern world, we need surprises, like a dragon in the apple orchard, to remember how the delights of magic.
CONNECTION: By housing a man made object, the garden is integrated into the overall home both symbolically and stylistically. It becomes another room in which to express your taste.
FOCUS : Similarly, our interior rooms have focus: A fireplace or television, a dining table, the kitchen counter, the bed. Garden rooms benefit from having similar focal points.
PURPOSE: Water features attract birds and provide soothing sound to block unwanted noise. Carved stone benches provide resting spots. Wrought iron arches guide you through the garden. Dramatic pots hold plants in spots where they might otherwise not grow.
Photo credit to 'Ollie Girl' (Donna) at Flickr
Last, and most important:
BEAUTY: This needs no explanation.
Photo credit to Kelly O on Flickr