Normalization covers more than just combining characters. CJK full width digits and punctuation can be problematic when you want the canonical forms for pattern matching:

  s = '１ ２'

  print(unicodedata.normalize('NFD', s))
  print(unicodedata.normalize('NFC', s))
  print(unicodedata.normalize('NFKC', s))

  １ ２
  １ ２
  1 2