It comes in both red and white and will give you that ultra sheer look. (aglamlifestyle.com)
Tip: You can also use a damp beauty blender to get that glowing, almost sheer look. (elle.com)
I think they're useful for a few reasons, one is to act as a «placemat» (but much easier to wash, in my opinion) and the other is for sheer looks. (makinglemonadeblog.com)