Often people will form their own LLC for their contracting work. Sometimes the customer/employer requires it as a condition of the contract.
Though it certainly looks and feels more like an independent contractor relationship if the person providing services, it does not necessarily make the arrangement legal. The Massachusetts Independent Contractor Law has three very specific requirements that must all be met to be considered a contractor rather than an employee. This statute does not mention anything about incorporation as an exception to the three-part test.
What this means is that you should consult an employment lawyer if you are unsure about the classification of your LLC as a contractor, or are using the services of an LLC as a contractor in your business.