A healthy balance between your personal and professional life is absolutely necessary, especially if you're starting a new business. It's important to keep in mind that most new small businesses fail. You'll have to work hard to make sure you aren't trading your personal life for your new professional life.
Your friends and family will still count on you to be there when you need them. The last thing you want to do is spend so much time on your business that your friends and family give up on you. If your business fails and you've cut everyone off, your support group could be gone when you need them the most.
Make sure you also pay attention to your personal finances. If you use your personal assets and credit to pay for your new business, make sure you aren't risking too much. What happens if you don't get that big deal? You could get stuck with a very large personal debt that takes years to pay off.
No business is worth sacrificing your personal relationships or your financial security. Make sure you're well prepared when you start your business.