What do consulting companies do to assist other companies with that these companies can't tackle themselves?

You can't tell the problem of a company if you are working inside of it and following their system/processes and or abiding on their rules & regulations. They get a consulting company in order to tell to them freely what problems they might going through or will go through or the problems they currently encounter. It's more on monitoring the company if it still follows its mission & vision. In consulting, you will be able to hear the truth about what's really the problem/wrong in your company that you also denying to yourself.

Hello Mr Al Shubaily

Consulting is a very helpful tool for a company to outsource work to a third party mainly to concentrate its effort and  focus on operations. the top5 things a company requires or prefers to hire a consultant I would say based on my field in Telecom are

1 monitoring and evaluation of a project

2 Quality assurance

3 call center operation management

4 Sales forces mainly telemarketing

5 employee audits to get a fair mediator between the employee and the employer.

:based on the company problem and the needed assets  which mostly comes throw the following field

finance  assistant- P&L, Banking, Reschedules loans and projects

Managerial assistant - Recurte- Employee and staff perormance Audit

-Evaluation Assistant- profit, Customer service 

Management consulting includes a broad range of activities, and the many firms and their members often define these practices quite differently. One way to categorize the activities is in terms of the professional’s area of expertise (such as competitive analysis, corporate strategy, operations management, or human resources). But in practice, as many differences exist within these categories as between them.

Another approach is to view the process as a sequence of phases—entry, contracting, diagnosis, data collection, feedback, implementation, and so on. However, these phases are usually less discrete than most consultants admit.

Perhaps a more useful way of analyzing the process is to consider its purposes; clarity about goals certainly influences an engagement’s success.