Contractions are useful in informal writing in many contexts, including informal letters, fiction and advertisements. Contractions help save space and give writing a friendlier, more accessible feel. However, experts advise against using contractions in formal writing, such as certain business, legal, academic and government correspondence and documents.
Contractions display a friendlier and more accessible approach due to their use in everyday speech. By using contractions, writing can read with a conversational quality, rather than feeling like a stiff legal document. Many fiction writers use contractions generously, especially in dialog, as not using contractions can make characters seem stiff and unrealistic. Most advertisements also use contractions, not just to create a friendlier feel, but to save precious space in slogans and advertising copy, which must be short and deliberate.
Two contractions should not be used in combination, such as contracting "He is not free" to "He'sn't free." Affirmative contractions, such as "we're," should not be used at the end of a clause. However, negative contractions, such as "haven't," are fine to use at the end of clauses. Even in some business, legal, academic and government situations, experts find contractions acceptable and advise writers to use their own judgement in these situations.