I think the usual reason for developing a short version of an existing questionnaire is practicality. Using shorter questionnaires can save time and money, and reduce inconvenience for respondents. This can be useful in both research and applied contexts. However, using a shorter version of an established questionnaire may result in reduced reliability or validity of scores.

Whether this is acceptable depends on context: I.e., how important are the decisions about individuals or research questions that will be made on the basis of the scores? What are the practical costs of administering the full-length questionnaire?