In the original gradebook, users had the option of clicking on an arrow by the name of an assignment and selecting "Assignment Details" which would provide additional details. See this guide: How do I view assignment details in the Gradebook?
However, in the NEW gradebook, this is no longer a feature. Our faculty made use of this information, and without it have a harder time assessing their assignments. I understand that you can go to the Speedgrader to find the average, and then sort the gradebook columns to see who did well/poorly, but these are just extra steps. The tool existed before, so this request is not for something new, but rather to bring it back.