If the variance was favorable then no need to investigate it . But when the variance was unfavorable the company must investigate about the reason .

There is a cost associated with investigating a variance. Hence companies rarely investigate all variances. All variances can be investigated. A favourable variance can indicate a competence and investigating it can lead to strengthening a competence. An unfavourable variance is investigated because it causes loss or cost to the organization and need to be rectified. Usually a small favourable or unfavourable variance can be due to business or economic scenario and unavoidable, Hence many organizations adopt Management by Exception where variances are analysed if they cross a certain threshold.