Let me show you what this means. The picture below has arrows pointing to the middle of the diamond. The arrows indicate the darker shadow that's visible in the center of the diamond. The dark shadow looks smaller in the center and then flares out on each end. It takes little imagination to see the shape of a bow tie in that shadow.
Now that you know about the bow tie, you might like it. Optical effects and inclusions are cool things. I've sold diamonds before just because the inclusions in them formed shapes that were meaningful to the buyer. If your father always wore a bow tie or you're in love with a man who wears one, a bow tie effect in a diamond can be a symbolic way to think of his love every time you see it. If you like the effect itself, then you should have one! If you like elongated shapes like pears, ovals, marquise or elongated cushion cuts, then don't let the bow tie deter you from getting what you want. Just know that a bow tie can present and remember that the price should reflect it if it is.
Many people believe that a bow tie creates a pleasing contrast between shadow and light, optimizing the diamonds brilliance. If you're one of those people, then you should have exactly what you want! It's up to us to determine what constitutes beauty. Diamond beauty, like so many other things, is in the eye of the beholder.