This article does a great job of summarizing some of the important ways that improving your personal well-being can help you grow and improve a successful law practice.  

How many solo attorneys do you know that work a 9-5? The ones who eat well, work out an hour a day then sleep a solid 8 hours at night.

Being a solo practitioner puts you in a position to actually reap the rewards of your hard work, rather than pass a big chunk off to the firm you work for. The flip side of a solo practice is the fact that you are responsible for more, including fee collection (that is, making sure that your clients actually pay).