Are you willing to assume this risk, if you bite on a hard piece of food or candy?
1-Usually, after advanced decay, a tooth needs a root canal. With huge cavities, almost all of the main part of the tooth is gone. This amount of damage to the tooth structure doesn’t let the dentist restore the tooth properly. A crown can help with the final restoration.
2-For cavity preparation, removing the roof of the pulp chamber is required. Otherwise, finding the canals and getting access for cleaning and shaping the canals is impossible. More explanation is available at my website page "Ask Your Dentist" https://www.atozdentalcare.com/ask-your-dentist/
3-Pulp chamber roof removal compromises