Sometimes purple is an attention-grabbing bully, like in this Smokebush. (No one steps into a garden and ignores its dark, brooding presence.)
Sometimes purple is dark-veined and gleams against a lighter shade of itself, like in these geranium. And sometimes, purple is velvet-edged and mysteriously deep, even in something as common as petunias. You sometimes have to bend down to appreciate purple’s ability to play well with others, like in this Japanese painted fern.
And purple stems, hazed with minute white hairs, are definitely worth a closer look, like on this cimicifuga. So whether your tastes run to things subtle or bold, purple can accomodate you. A garden without purple is quite simply, wrong.