Wisdom teeth. Wisdom teeth, even impacted wisdom teeth do not 'ruin the rest of your teeth'. First, most dentists agree that they cannot produce crowding of the other teeth. Second, they can cause local problems such as cysts, infections, swellings, pain, and on rare occasions destruction only of the tooth right in front of them. All wisdom teeth, if potentially problematic should be removed at age 16-19.
Space. We look to see if there is enough space for the wisdom tooth to erupt and function normally. It it is in a good position and can be cleaned easily then it is not removed. If there is not enough space or if it is interfering with an adjacent tooth then it should be removed. This will keep the remaining tooth healthier.