In a Classification Query, what's the difference between classification with "Hierarchy" and without?

When searching for patents in a query with classification (hierarchy), the search results will include not only the patents in that specific subgroup but also those found within its child subgroups. Take IPC as an example; a hierarchical classification query that includes ICLH/(G04B11/00) will result in the patents in the subgroup of G04B11/00 and its child subgroups G04B11/02 and G04B11/04. On the other hand, without hierarchy, a query including ICL/(G04B11/00) will end up with those patents in the subgroup of G04B11/00 only.