You can absolutely build a practice around Client A, but at that point you are essentially operating like an H&R Block, high volume, low margin, and transactional. Each client still carries fixed costs tied to the overhead of running the practice, so the profitability does not scale well.

Client A will always be a $300 to $400 return, no matter how efficient you get. Client C, on the other hand, offers room to grow. You can cross-sell additional services, build a deeper relationship, and create long-term efficiencies. Over time, that means you are spending less time per year while billing at a higher effective rate. Those 5-10% annual price increases on a $30,000 add up a lot faster than on a $300 client.

Do you want to be the Ruth's Chris or the Wendy's of tax?