There is a relatively simple explanation at http://understandinggrammar.com/sentenc ... s/clauses/
I suppose that knowing this grammatical naming of parts is useful. It provides the teacher with the tools to explain complex sentences composed of parts that can stand alone, and parts that cannot, and the role of linking words and punctuation in making the whole understandable and unambiguous. This is particularly useful in teaching writing to native speakers, but probably a lot less so to non-natives who are still figuring their way through basic usage patterns.
So, what is important about these grammatical descriptors in terms of English-language learners? In my view, only this:
1.The fundamental characteristic of all these types of clauses (and I agree, deciding which type each one is can be confusing) is that they are dependent clauses.
2. Whatever their specific names, dependent clauses need to be properly coordinated with their corresponding independent clauses. This take place with good punctuation skills and the good placement of relative pronouns and adverbs, and subordinating conjunctions.
3. As is the case with native speakers who couldn't begin to do this grammatical parsing if their lives depended on it, but who for the most part speak and write the language correctly, second language learners need lots of practice to the point of internalizing the common English language structures.
4. At that point, this kind of precise language about language becomes a useful tool. Until then, in my view,(1) and (2) seem to be all we need to know about dependent clauses.
Put another way, good technique is more important than technical language, and we don't need a lot of the latter to be proficient at the former.
What do you think?