A few moment's reflection will showus that if our pieces are too large, we shall not have the same•opportunity of building up. The process of summarising orbuilding up is in fact restricted by the size of the pieces,generally speaking the smaller the pieces the better the chanceto build up. Too large pieces will preclude us altogetherfrom reporting on smaller subjects.
Here Kaiser touches on the broader themes inherent in the concepts of atomic notes, which might be used to build up new and interesting structures. He doesn't specify the "size of a note" nor does he say that one will "know it when they see it", but he's suggesting something very close to it.
Rather than define the appropriate size, a feat which is difficult to do at best, he's providing a very narrow set of benefits for encouraging one to cut things down to size as they index them: small pieces are easier to use to build new things.