This view shows individual objects that retain most of memory. The objects are shown as a dominator tree. That is, if object A retains object B, then object B will be nested in object A's node. Read more about retention.
This information can be useful to explore and reduce memory usage. In particular, it helps finding memory leaks caused by individual objects. Sometimes you can learn a lot by looking at memory distribution in terms of individual objects.
Also consider "Class list" which shows similar information for objects grouped by classes.