In most cases, yes, a business usually needs some type of registration before operating legally. The exact rules depend on where the business operates, what it sells, and how it is structured. Even small side businesses may need local licenses, tax registration, or a formal business entity.
If a business operates without required registration, there can be risks. These may include fines, tax penalties, problems opening a business bank account, contract disputes, or personal liability if someone sues the business. In some cases, the business can still operate as a sole proprietorship without forming an LLC or corporation, but other registrations may still apply.