Both of my DSs (now ages 21 and 18) each only had 3 wisdom teeth develop. They both had theirs removed this summer.
DS18 never had a problem and thought his wisdom teeth were coming in just fine until we saw the x-ray and saw that one of them was laying sideways in his jaw and eventually would've eroded and ruined the roots of the adjacent molars. What he thought was the top of the tooth coming in straight, was actually the SIDE of the tooth, protruding through his gum. He recovered easily, except for dry-socket in the one area where the tooth had been laying sideways down in his jaw and needed a bit more extensive incisions for removal.
DS21 started to have trouble with his wisdom teeth this past year, so he was relieved to get his 3 removed. He didn't have any trouble with recovery at all, no dry-socket.
I agree with the previous posters who say that wisdom teeth removal, especially on the advice of professionals, is one of the best preventative moves you can make for your children's oral health into their adult lives.
Also, if your child is still on your dental insurance, even more reason to not put it off. For example, DS18 is a full time college student so he is still on our dental insurance and his was covered except for about $225. DS21 no longer has dental insurance, so his cost was about $1075. If only we had made sure to have his removed while he was still on our dental insurance, it would've saved him a lot of pain, and money. We planned on him having them out the summer after his senior year of high school, before college, but it just never got scheduled.

Lesson learned, which is why we made sure that DS18 had his removed this summer before college started.