Using a visual metaphor can be good for providing a consistent look to a
web site, by providing something familiar and making users feel at home. From
grandma's kitchen (example 1) uses the visual metaphor of index cards
that might have been in your grandmother's recipe box. Consistent repetition
of a well-executed visual metaphor makes it difficult for the visitor to get
lost; however, poorly-chosen metaphors can be confusing.
A consistent visual theme can work just as well as a metaphor. A site can
be photographic or hand-painted, primitive or futuristic, art deco or gothic,
juvenile or mature. Recipes for today's
kitchen (example 2) uses the visual theme of kitchen appliances (in
this case, an oven).