Why would reducing employee turnover be good for the client?

When a client approaches a business, he wants to see a organization with a skilled, motivated and experienced work force. having employees that are happy to be at work, causes them to... well be at work. They don't quit, they don't call in sick, and they don't slack off in the job (as much). This produces a workforce that has a lower turnover and in turn a workforce that produces higher quality products and services. Turnover is something that also hurts the company's long term future. It is always better for moral and for the overall well being of a company to promote from within. With a high turnover that is not always possible. A company with a solid internal promotion culture and low turn over will be more likely to succeed and make a better service provider for any client.

Clients are provided with better service when the employees are veteran, well-trained, experienced help. Employee turnover prevents the employer from building a quality staff.

Time spent on training and processing paperwork.

Reducung Turnover accomplishes three things: reduces labor cost, increases experience, and improves goodwill. Labor costs are reduced on two dimensions: training expenses are increased with higher turnover. Also, someone has to do the training. Unless they are a full time trainer, the trainer is probably there to do something else that adds to the overall bottom line.
Experience is the net sum of the companies knowledge-base. Everyone brings unique knowledge to the firm and take it with them when they leave. The 'smarter' the company, the more flexible and adaptable it is.
Lastly, employees and ex-employees are ambassodors of your product or service. They may be future customers. The higher the turnover ratio, the lower the opinion of the firm among employees, ex-employees and , indeed, customers.

Low turnover means that employees are happy, and have had the opportunity to complete their learning curves and become very productive.

When an employee leaves, the company must pay for recruitment and training, and deal with low productivity for weeks or even months. Also, not every new employee works out. A company may have to hire several employees to get a good fit and an employee who will stay.