Sentence formation is one of the key ingredients to good writing. There are several forms of sentences you can use in your writing - simple, compound, complex and compound-complex - and knowing how to use all of them will allow you to express your ideas with clarity and in great detail. You'll also be able to add variety to your work to keep the reader interested.
Of all sentence constructions, compound-complex sentences are typically the longest and most involved. This is because they combine two different types of sentences into one long sentence. To be specific, a compound-complex sentence unites a compound sentence with a complex sentence.