I always use them to display my personal best pieces. But to be honest, if people don't like my stuff based on my featured items, then they probably don't like my stuff. I don't list things in my shop if I don't like them, so I like to think that all my products are as good as eachother, so if you don't like 4 of my items, you probably don't like the rest.
I think the featured listing thing is great, because a shop can use it to display their best pieces, their holiday pieces, or perhaps if they're feeling daring, the pieces that just aren't selling (though that may turn people off). I think it's a pretty good idea to take advantage of it because it also increases the listings visible on the first page by 4, and can help people get a better idea of your work if they prefer to view shops as a list than a gallery.