A client can bring in more money in total yet need so many hours that it crowds out more profitable work. Comparing total profit and profit per hour shows both sides.
An example with numbers
Client A contributes $2,000 after direct costs and needs 100 hours. Client B contributes $1,500 and needs 50 hours. A leaves more money in total, but B brings in $30/h against A's $20/h.
Try it with your numbers
Enter each client as a line. Then divide their contribution by the hours spent and check whether you could use the freed-up hours for other work.
Example figures for learning purposes. They are not a recommendation and do not replace professional advice.