Using online advertising is amazing for applying one of the core principles of marketing – creating an urgency. Host a sale, email or IM your customers about it and tell them it’s short-lived. They must come in now, or they’re going to miss it.
You wouldn’t really be able to do this with offline, classical ways of advertising. If for example, you gave away fliers or put up banners, the sense of emergency would be lost. Patrons would then have time to think twice about walking through your front door.