If kicking is any part of your repertoire, even a small part -
We all know that if you throw a kick higher than your flexibility allows, that kick will be weak. (I'm not taking into account balance issues) Whatever your range of "kick height", that top part of it is going to be the weakest part of your range because you are fighting your body trying to get it up there. Let's say you are flexible enough to get your foot up around the height of an opponents chest. The height where you can generate any real power, as well as a smoothness in kicking, is going to be somewhere lower than the chest, let's say around the lower abdomen. If you can become more flexible, you can raise the height of where you can generate power. It's still going to be lower than how high you can swing your leg, but that "power point" for lack of a better term, will raise somewhat. It allows more options in kicking. At least more options with some semblance of power.