Adults can have up to 32 teeth, with the wisdom teeth being the last to appear. They usually appear at the age 17-25, although sometimes they appear many years later.
Wisdom teeth, if impacted, due to lack of space/room to come through, can cause discomfort such as swelling and soreness of the gums growing around it (as a result of food trap and bacterial growth); impacting against the tooth at the front leading to possible development of gum issues and/or deep decays.
While most wisdom teeth may not cause pain, its elective removal may be advisable especially if they pose potential risks to the tooth at the front. In addition, they are situated at the very back of the oral cavity that gaining access for efficient clean is literally impossible, thus its presence is only to create a niche for bacterial growth.