To remove impacted wisdom teeth and non-restorable teeth
Orthodontic purposes--e.g., if there's not enough space for the tooth
Loose teeth that are grossly decayed
Fractured teeth that cannot be repaired
Roots that remain in the jaw after a tooth has been fractured
Preventing bone loss—If I need to extract a non-viable tooth, I almost always recommend placement of bone substitute in the area in which the tooth previously occupied. The reason is that you can lose up to 40% of bone that previously existed around the root of the tooth within 6 months to a year if the socket isn't filled.
Proceeding with an implant—After tooth extraction, continuing with a dental implant is becoming more common.