You should treat your business as though it were a living entity. It needs to be nurtured. All living things are continually regenerating themselves and discarding old, worn out cells.
Same with your business, it will lose customers through natural wastage so you should always be taking on new work to counteract this. When it reaches the stage where you can't cope, then think of ways of changing things for the better. If you stop this process there is a very real possibility that your business will suffer.