Why do you feel internal auditors have an important role in the company?

Internal Auditors are important because

1- Internal Audit focuses to look for deficiencies in the system/Processes to mitigate the over all risk of the company; which in return helps to mitigate the risk of fraudulent activities within an organization.

2- Ensure compliance with company's policies & policies of any regulatory authorities.

Internal auditor's role is important, because upper level management is relying on his judgement about controls. They have made him responsible for evaluating internal controls and report on deficiencies and ongoing fraudulent activities. 

Thus his report is an important factor in BOD decision making and so it may be said that internal auditor can help improve organization's performance. 

Internal Audit's objective assessment and reporting on the adequacy of an organisation's Enterprise Risk Management framework is at the centre of it's important role. The latter can be most efficiently and effectively performed as the '3rd Line of Defence' in an organisation's Governance/Risk/Compliance model designed to achieve robust corporate governance. (Please refer to my other related answers for a more detailed explanation of how Internal Audit should perform this '3rd Line of Defence' role).