Gravel gardens exist in many forms and seem to divide the garden community- some love them and others hate them.
The reason for using gravel is to fulfill two roles. Firstly to act as a mulch to suppress weeds and retain moisture and secondly to provide an interesting and textured background for the planting and other features. Sometimes the gravel is laid directly on to the earth so that each season new arrivals can add to the garden(or not!). But many gardeners opt for a weed suppressing membrane under the gravel which lets the water through but prevents weed growth. This can create an attractive and very low maintenance garden.