Halos make a diamond look bigger.
This makes a halo element a perfect way to accentuate a center stone without spending as much on a larger stone. A diamond twice the size is much more than twice the price, so a halo can help create a bigger look for less cost.
Halo settings protect the main gemstone.
Although diamonds and sapphires are two of are natures' hardest substance, the thin outer edge can be chipped if it is hit against a hard surface.