My research which is about to publish shows the internal communication is catalyst in organizational performance. if you are interested...we will share more..

Numberless.  My paper on Internal Branding and the research I have recently conducted reveal and highlight the pivotal role of internal communication in the achievement of organizational goals, mission, and overall company performance. Top-to-bottom and side-to-side communication are key to overcoming departmental barriers and popping these "bubbles" that prevent synergy, coordination and alignment of values. 

As Maria Matiatou suggests, they are numberless. Some are readily quantifiable (e.g. opportunities for cost-savings and for raising revenues by operating more efficiently and effectively), while others are less readily measured (e.g. improved staff morale and wellbeing; enhanced external reputation as the positive results of better internal communication reverberate more widely).  I've attached a link to our textbook on organisational communication and would recommend you look at topics such as communication audits, which can yield real benefits.

Book Effective Organisational Communication: Perspectives, Princi...

As Maria Matiatou suggests, they are numberless. Some are readily quantifiable (e.g. opportunities for cost-savings and for raising revenues by operating more efficiently and effectively), while others are less readily measured (e.g. improved staff morale and wellbeing; enhanced external reputation as the positive results of better internal communication reverberate more widely).  I've attached a link to our textbook on organisational communication and would recommend you look at topics such as communication audits, which can yield real benefits.

Book Effective Organisational Communication: Perspectives, Princi...

the bennefits are inquantificable. you can see that with sugestions above. i'd like to suggest you to understand the organizational communication as a total pack - internal anda external;  as we can ask "integrated communication", in a global perspective.  The truth is that´s impossible to dissociate them into the organization. In practice they work like a whole. 

i sent you an academic work, a thesis. I think it is better than a published book, because it has an accessible language, it works directly the subject and gives you some biblio references you can search as you like. 

I hope i can help you. Good work!

I'd agree with Anabela that you need to treat internal and external communication as closely interconnected - though in practice the integration is often missing, both in published work and in organisational practice. Good luck!

Dear silini, If you do not have effective internal communication, your organization will be a numb entity. Therefore the benefits of an effective communication are numberless as my other colleagues have mentioned.  In terms of benefits you have to look at various levels. At the CEO level the buying in  to gain the confidence of the employees to his  leadership is vital. A CEO who does not communicate is  a dead CEO. But  the channels and the  kinds of messages used  by the CEO to his top management, the middle management and the  line staff will be different  to understand their background.But  at the second level the middle management need also use different  kinds of  communication to the other  employees and to the top management. 

There are numerous books and article that you can make references to  on this topic

A point I wish to make is that reference to internal communication  does not take consideration cultural factors. An Japanese, Chinese  and Japanese companies establishing themselves in  another society find the internal communication  with their ordinary employees difficult because of cultural inhibitions embedded in the internal communication. Experts in organizational communication  may need more time to dwell on this subject. Conflicts  occur when one word may symbolize a different meaning to another group of employees.

• Boost morale -- keeping staff in the loop demonstrates respect for them, reinforces "teamwork" as essential to organizational success
• Reduce rumors -- timely information counters unhealthy speculation about what's going on.  Remember, anyone part of the organization will find interesting news they can use or that in anyway relates to them.  That, by the way, is just about anything that goes on in the organization
• Improve external relations--strategic engagement of staff supports public relations and engagement by improving chances of a consistent message from the company.  by the same token, satisfied or at least well informed employees are less likely to bad-mouth the organization and, on the contrary, are far more likely to defend it.

Others have done a good job showing how organizational efficiency, productivity, and innovation are well served by optimal internal communication.  Trust, respect, loyalty, and security are all sound environmental qualities management should want to foster and expand.  Communication makes that possible.

See it also from the angle of  identifying which publics of an organization that are serviced with internal communication such as employees, management, shareholders, etc. then it is easy to think of the benefits of communicating with each of these groups. 

it may help the employee to have a good working environment. in addition, effective internal communication also contribute to no barrier between employer and employee within organisation