The first advantage is that the frequency distribution is much flatter than that of individual letters (though not actually flat in real languages; for example, 'TH' is much more common than 'XQ' in English).
第一個優點是頻率分佈比單個字母時更平坦（雖然實際上並不平坦，因為在日常語言中，“TH”就遠遠比“XQ”常見）。