Leaf coloration in some plants is more pronounced in spring, fading as the season progresses. The color leaves change in the fall is a valid addition to our palettes, but it, too, is fleeting like the flowers. In addition to our basic leaf color palette, plants provide us with built-in color contrast when they have variegated leaves. Some variegations are bold, whether abstract or quite regularly patterned. When bold color is combined with a large leaf, the plant creates a definite presence in the garden.
Some people dislike all leaf variegation intensely.
I love it. Nothing brightens a dark corner like a variegated leaf. Yes, you do have to use them judiciously. But this is true with all color, in all media. Pure leaf color is only one of the tools plants give us to create beautiful gardens.