"Why an LLC?"

There are some professions where it's standard to form an entity, especially in the medical field. Some States require doctors to be Professional Corporation as PC or PLLC. Florida uses PL. A Professional Limited Liability Company (PLLC) is a specific business entity designed for licensed professionals—such as attorneys, accountants, doctors, and engineers—to operate while providing liability protection for personal assets.

Some vendors or service providers will not work with Sole Proprietorships.

Some people form an LLC in anticipation of holding property, getting partners, wanting some benefit plan which requires it. Your State likely has business registration requirements, but not all States have the same requirements. My State is looking to "lower the bar" on being in business as a professional. "The purpose of the Task Force is to provide the Governor with recommendations and strategies...to reform the professional occupational licensing system for the purposes of identifying and removing barriers faced by licensees that are not necessary to protect the public and improving access to and availability of professional services..."

Most of this is Legal, not tax related.