This is a really important question, as all too often the project manager is focused on the outcomes of his or her project, without due consideration for the wider issues.  I advocate that PMs need a greater focus on the 'landscape' within which they are executing 'their' project - I refer to this in my lectures and publications as 'wider business awareness'.

To some extent this is tied to reward structures: if a PM is rewarded for delivering 'their' project, then they tend not to consider the 'wider' picture.  However, there is little to be gained by saving $10,000 on your project if it costs $50,000 on two or three other projects, or elsewhere in the organization.  Reward therefore needs to be tied to the delivery of the 'wider' requirements of the organization.

Keeping a watchful eye on the business is also about 'culture' - the organization has to be transparent enough to ensure that employees (PMs in this instance) have enough information to understand the wider picture.  This means a free flow of information, and some organizations are uncomfortable with this level of transparency and communication.

I hope this helps...

I agree with Steve's answer above, but there it is hard to apply this when most projects are nowadays outsourced and the project manager more than often is from the external organization. The only way that an organization can benefit from what Steve describes is by appointing a Business Case Manager that works along with the project manager to capture the knowledge that emerges from the project and to ensure that the organization's wider objectives are served by the project.  

There are some interesting points made by Elias and Stephen,

The size of company is important. Rolls-Royce plc have project managers,  business managers and programme managers. Between these three project costs and benefits to the company overall are covered. (each manager has a well defined job description so there is no overlap or duplication.

In a smaller company, if the Prince2 process is followed, the initial project proposal should cover the business case, so as long as the project objectives are met and the rest of the business keeps on track, business performance should (in theory) be maintained. If one project goes off track, then the review gates should pick this up and the process then allows escalation to the person responsible for delivering the business benefit, usually a director.

Steve, Elias and Paul, thank you for your quick and interesting answers.

The project manager must ensure that production line is balanced with the allocation of resources to align with the specified activities sequentially arranged towarded the completion of a named project.This helps to avoid timeoverun and costoverun implications.He is responsible for planning,sheduling control and monitoring

The main role of Project manager in relation to the business case is an "umbrela view". It is very important that PM has to have general experience and knowledge of project of business case. Of course he/she can have more knowledge in one part of project bud he/she has to be introduced in all segments of project. Why? Because he/she will easily detect if some results of BC are incorrect or if they have no sense.

If PM has very strong knowledge in (let's say) 70% of details of project, he/she can miss out some illogicals of BC results.

Because of that PM has to have an "umbrela view" to the project. 

The business case is typically defined before the project starts. The project manager's role should be to critically evaluate the case, offer improvements and refinements, and most important, implement the right process and policy in his/her project to realized the intentions expressed in the business case. In other words, make it work and success. And finally, if conditions change along the way the PM must adjust the business goals, discuss them with the team and management and revise the business case so that business success is indeed achieved!

demonstrate the project value through business case.