  Effective peer code review in collaborative software development necessitates
useful reviewer comments and supportive automated tools. Code review comments
are a central component of the Modern Code Review process in the industry and
open-source development. Therefore, it is important to ensure these comments
serve their purposes. This paper reflects the evolution of research on the
usefulness of code review comments. It examines papers that define the
usefulness of code review comments, mine and annotate datasets, study
developers' perceptions, analyze factors from different aspects, and use
machine learning classifiers to automatically predict the usefulness of code
review comments. Finally, it discusses the open problems and challenges in
recognizing useful code review comments for future research.
