hey this is a interesting question, it can be tackled in many ways,
1:clinically: if the tooth is loose how loose, if the tooth is root treated generally crowning the tooth for protection is the treatment if choice. but if the tooth is so loose that the dentist feels it is not going to last a year is it worth crowning the tooth!
2:emotionally: if the tooth is closer to the front of the mouth in the smile arch, whether the tooth is loose or not it may have discoloured quite badly and the patient may want it crowning for cosmetic reasons even if the prognosis is poor for the tooth long term.
as you can see just two reasons why there are arguments for and against the question. at the end there is no right or wrong as long as the patient is well informed by the dentist of all options available and the patient can then make a well educated decision.
Dr Kailesh Solanki
kissdental
www.kissdental.co.uk