If you have wisdom teeth and they haven't come in normally, you need to have them removed. And possiblly even if they have come in. They are so far back it's very hard to keep them properly cleaned. It's better to get them removed as a young adult rather than an older person. It's also better to get them removed before they start causing problems.
Most dentists recommend to extract wisdom teeth, even if there are no symptoms, to prevent future complications.
For adults over 30 years old, most dentist would not remove wisdom teeth because the roots are completely formed and the bone around them is dense. Extraction would be indicated only if there are symptoms.
It is not necessary. my dad's wisdom teeth are all still intact and he has never had a need to take them out.