The idea of the clause is fundamental. A clause almost always contains a subject and a verb, and most clauses contain other elements as well. A main clause is a clause that can stand alone as a sentence:

I play in a band.

Simple ideas can be expressed simply. If the ideas are powerful, simple phrasing will only strengthen them, by making clear that the power doesn’t come from fancy wording but from the idea itself.

All the same, a series of simple main clauses, one after the other, sheds no light on any relationships that you, the writer, perceive among the ideas or information you are sharing. To show relationships among ideas and information, it helps to have the full array of sentence structures at your command.