protect your personal assets from liability. It's not tax savings move (LLCs are pass through entities), it's a way to limit your liability (hence the "limited liability company" name). It's not required that you do it. Although companies may take you more seriously if you have an LLC. Makes it seem like they are contracting with a real company instead of just some guy. Plus they can tell you are careful/thorough enough to take steps to "do it right" with an LLC. So maybe there is some marketing advantage to having an LLC.

They cost money to set up to and maintain on a yearly basis. You'll have to decide whether the benefit outweighs the cost.