but what use is type 1, type 2 and type 3?

Like many of his re-inventions of the wheel, I think what Dale was trying to capture is what linguists call register. Some dictionaries will tell you what a word's register is, i.e., if it is formal, slang, colloquial, jargon, etc. Speakers use different subsets of language (accent, or pronunciation, vocabulary choice, etc.) depending on the context in which the utterance occurs. Good authors to read on this would be Halliday, Labov, or Trudgill. Historically, one of the big differences between descriptivists and prescriptivists is using less judgmental names for register; cf. the big flap over Webster's Third International in the early '60s.

Ceci n'est pas un seing.