My writing group has struggled with this issue. In the past, there’s been some disagreement about how to structure the feedback process and whether a structure was even necessary. Ultimately, we did develop a structure for providing feedback. However, it has changed over time based on the needs of individual writers.
Readers have lots of different things to say about individual written pieces. Without structure, there’s a risk that critiques can meander without direction and leave the writer confused about what works and what doesn’t. In addition, without structure, readers can get caught up in copy-editing or in critiquing the minutia of a story, leaving the writer without a clear idea of what to work on.