In grammar, a clause is the smallest grammatical unit that can express a complete proposition. A typical clause consists of a subject and a predicate, where the predicate is typically a verb phrase – a verb together with any objects and other modifiers. However the subject is sometimes not expressed; this is often the case in null-subject languages, if the subject is retrievable from context, but it also occurs in certain cases in other languages such as English.
English is a right-branching language. To build a complex sentence, you need to add clauses and expand your ideas. By using relative clauses properly, you can vary the length of your sentences and build a music, a melody. Otherwise, unbalanced writing would only produce a set of words.