Although people spend more time in oral communication, written communication is more effective under the following circumstances:
Conveying complex information: When the sender wants to convoy complex information, written communication serves better than oral communication. Having the written document, the receiver can read it repeatedly, until, he/she understand the entire message.
Need for permanent record: Written communication is preferable when a permanent record is needed for future references.
Communicating with large audience: When the audiences are large in number and geographically dispersed, written communication is fruitful there. The sender can communicate repeatedly with the same written document or information sheet.
Less need for interaction with audience: Written communication is also suitable when immediate interaction with the audience is either unimportant or undesirable.
Maintaining uniformity of application: When any message is to be applied uniformly at different places, the sender should prefer written communication instead of “oral communication”.