They protect a boots tongue from being worn into by the laces, especially when using a particularly durable lace which can be more prone to doing this.
They can also add a tad bit of thickness to the tongue and help snug up a fit just a little.
I can understand not liking the look ( I don't like dress boots or cap toes ), but most people can actually benefit from them at least to some degree.
I have low instep and skinny ankles, so kilties often help snug up that area. My feet are like duck feet, wide up front and low volume, so kilties help refine the fit, and I personally love the look too!