Users' selective employment of computers has been studied on the material of logical problems differing in the degree of complexity. The work in the "man - computer" dialogue condition is found to be most effective when solving problems of medium and high complexity and when the general emotional attitude to the help from a computer is positive; however the process of solving especially difficult problems exhausts the user. Efficiency in the employment of computers must be assessed not only by temporal criteria and the number of correct answers but also by the penetration into the content and into the performance of the task.