The descriptions of some salad greens mention that the leaves are frilly and add bulk to salad mixes.
I assumed that was to be able to use less.
However, I've now discovered a different reason. I bought one of those clear plastic boxes of triple-washed organic salad for half-price because it was at its use-by date. Today it is three days past, and a lot of the flat leaves are mush, particularly the baby beet leaves.
So - frilled is definitely best.
Victoria, British Columbia, Canada a cool mediterranean climate - rainy winter, dry summer