Here's a useful article written for the small business owner about when you should call a lawyer.
http://www.microsoft.com/smallbusiness/resources/finance/legal-expenses/7-good-reasons-to-call-a-lawyer.aspx#goodreasonstocallalawyer
It lists starting a business, collecting debts, and resolving business disputes. A theme is that it makes more sense to get legal help from the beginning, rather than wait for something to go wrong before seeking advice. It is almost always less expensive to get help up front, because once the horses are out the barn door, it is much more difficult to corral them.
There are also employment-specific reasons to get legal help at an early stage: firing someone, offering severance benefits, and drafting or evaluating non-compete agreements. Another is employee handbooks. No matter what you may hear, in most states drafting an employee handbook is not a game for do-it-yourselfers. Don't be penny wise and pound foolish in these respects.
