As a sole proprietor, you and the business are the same legal entity, so the trademark is effectively both a personal and a business asset. If you later incorporate, the trademark will need to be transferred to the new entity through an assignment.
An LLC holding the trademark separates the asset from your personal legal exposure and makes it easier to bring in partners, investors, or eventually sell the business. The trademark transfers with the LLC rather than requiring a separate personal action.
For most founders who intend to grow the business, registering the trademark under a properly structured legal entity from the start avoids the administrative step of a later assignment.