Why bother with garden edging? Why not just let plants grow up to the edges of lawn (if you have it) or of paths? Unfortunately, soil and mulch migrate from garden beds because of rain or birds which love to scratch in it. And some plants send their roots further than the bed and, conversely, some lawn grasses will enter your garden beds. Some sort of edging is necessary if you want raised beds.
There are many forms of edging commercially available, but they differ significantly in their sustainability. However, natural or recycled materials make excellent edging and can add uniqueness to your garden as well as minimising manufacturing impacts and waste going to landfill.