Wherever appropriate, correct grammar and syntax should be incorporated into advertising and copywriting. When correct grammar is used, sentences tend to be less confusing and the intended meaning is clearer. However, it is not always necessary.
Copywriting and advertising will usually have two goals 1) send a clear message and 2) compel the reader to act.
As such, advertising copy should more closely reflect conversational speech than the Oxford English Grammar book – but do try to avoid common grammatical mistakes such as split infinitives and lost apostrophes.