This video shows three high kicking drills. The first is simply for impact. The second to encourage speed in getting the foot off the floor, and back to the floor. The third is for balance.
High kicks are not practical for self-defence, but they should be included in practise (if possible). I don’t believe everyone is built to kick high, but we should all aspire to increase our individual flexibility, strength and technique. This way we all kick as well as we possibly can.