There are many reasons why one might require their teeth to be crowned.
restoring the damaged teeth
supporting teeth with major cavities or multiple smaller cavities which can't function with mere fillings
building a tooth post root canal treatment
correct the occlusion or biting patterns so as to uniformly distribute the forces inside the oral cavity
smile designing of badly discoloured or malformed teeth
form the pillars of the bridge while replacing a missing tooth
reshaping a tooth to correct its position for closing the gaps