Documents tell us before we write documents, we must state our purpose. Who should read those documents, don’t waste the reader’s time.
Punctuation tells us that we need to choose the right sign. if two sentences have a connection, we should use semicolons; if the connection is a sequence, we should use commas; if the second sentence is used to emphasize the first sentence - em-dashes; if the second sentence is minor points (parentheses).