Why comment at sprint level?
In Agile development, each sprint consist of some sprint specific details. There are times when team members may like to give comments related to the progress or issues pertaining any specific sprint. Those comments could be related to sprint planning meeting, sprint review meeting, sprint retrospective, sprint goal or sprint statistics etc. To add a comment to the Sprint, press the Comments button. The comments feature can be used as Scrum meeting notes, or for Sprint related conversation between the team members. It is especially helpful for teams which are not geographically collocated.