There are two disadvantages of classifying. First, if you classify pieces according to existing classification criteria, the structure obtained by the KJ method is the same as the existing structure. Suppose you have pictures of various kinds of flowers. You classify them according to existing biological classification criteria. For example, an apple, a rose and a cherry-blossom are all “Rosaceae.” You make a nameplate “Rosaceae” for the group.
By this activity, you get the classified information according to the existing classification. You do not create a new structure. This activity is not the group organization of the KJ method. If you really want the classified information, you do not need to do the group organization. For example, you can write the classification criteria on a whiteboard and place each picture on it efficiently.
When you use existing classification criteria unconsciously, you may smoothly pass the group organization phase without noticing the mistake.
However, in the illustration(A) phase, you have nothing to do but to draw a box that “these flowers are all Rosaceae.” You have no structure except for the existing criteria. There are no stories based on your experience. So you suffer in the documentation(B) phase. You have a list of boring facts only. For example, “There are Rosaceae and Leguminosae. There are A, B, C in the Rosaceae. There are D, E, F in the Leguminosae.”