Who is more important to growing your business, customers or employees? The answer is BOTH!
Customers want quality services and products for their money. If they find it at your establishment they will stay. If they don't they will move on. Your employees are a huge part of what determines that. If you treat your employees right, it will naturally bring in more business.
Let's take an auto repair shop for example. It is obvious that the staff at the front desk should be polite, dressed well and knowledgeable. The reception area should be clean and organized. That is where customers first interact with your business, it is your "packaging" and it makes your first impression. (Look here for an article on packaging your service based business) But what about the actual garage area?
If you have a dingy, dark and dirty pit of a garage, how will your mechanics feel? You will likely hear them complaining about the time they spend there. If they are complaining, do you think they are putting 110% effort into the job they are doing on your customers' cars? Not likely. They are probably doing the minimum just to ride out the time until they punch out.
Instead, provide a clean, bright garage with all of the modern tools needed. Then, the mechanics will be in an environment that allows them to enjoy their job. They probably got into it because they like cars, now they can work on the cars they love in a place that is comfortable for them. Then guess what happens ... The quality of their work improves because they are enjoying it! Skilled mechanics are attracted to your garage because they hear that it is a great environment to work in! Customers tell their friends how great of a job was done on their car! More business comes through the doors.
You rely on your employees to represent your company in every sense. Pay them fairly and provide a positive environment for them to work in. You will reap the rewards in more customers and a growing business.