Wisdom teeth often need to be removed because they frequently come in at an incorrect angle and many people do not have enough room in their mouth for them. It is thought that long ago in human history there was enough room for the third molars. Also, we guess that tooth loss at an early age was more common long ago, which lead to the need for additional molars in the late teen years of life.
When we say that a tooth is going to be impacted, what we mean is that as the tooth erupts from the jaw, it will come into contact with another tooth or dental structure that it should not contact. An impacted tooth is often the cause of significant discomfort and usually, leads to an infection.