Many tasks (and people) are still better suited to manual methods of working, for example a single quick calculation may best be done mentally or by using a pocket calculator.
Many people also prefer communicating face to face with their colleagues, rather than using tools such as e-mail. People may prefer to interact both to fulfill social needs and become they find this form of communication more effective. Example use of body language, tone of voice etc
The use of poorly designed, computer systems, or using “good systems” with inadequately trained users, will result in inefficiencies that negate the benefits computerized processing should bring.