When you search for patents in a query with classification (hierarchy,) the search result will include not only the patents in that specific subgroup, but also those found within its child subgroups.
For examples of IPC: a hierarchical classification query that includes ICLH/(G04B11/00) will result into the patents in the subgroup of G04B11/00 and its child subgroups of G04B11/02 and G04B11/04.
Without hierarchy, on the other hand, a query including ICL/(G04B11/00) will end up with those patents in the subgroup of G04B11/00 only.
