Crowd the adjoining teeth. If wisdom teeth cannot find enough room to come in properly, they will probably crowd or damage nearby teeth.
Your dentist will probably recommend wisdom teeth removal surgery if they don't completely arise. Some dentists have an opinion that it's wiser to remove wisdom teeth at a younger age, before the roots and bone are fully formed; and when recovery is often faster following the surgery. Having said that, certain young adults have their wisdom teeth pulled before they can cause serious trouble.