A dental crown is like a helmet that goes over the tooth and protects the underlying tooth structure - providing a predictable long term restoration for a weakened tooth.
Yes! Teeth that have deep fractures and are crowned can still experience further propagation of the fracture resulting in eventual tooth loss. The crown does not guarantee the tooth will not fracture but it does minimise the risk of it doing so in comparison to other restorative procedures available. Teeth that are very heavily fractured and have a doubtful or guarded prognosis would benefit more from implant placement than crowning.