A company is a separate legal entity and comes with formal statutory duties after incorporation. A sole trader business-name registration is tied to the individual carrying on the business.
It may fit an individual who wants a straightforward operating structure and does not need the same separation or governance structure associated with a company.
It may fit owners who need a separate entity, expect more formal ownership arrangements, or are building for a scale that warrants company administration.
The registration cost matters. The larger issue is whether the structure matches the way the business will own assets, sign contracts, take risk, bring in owners and meet continuing filing obligations.
For legal, tax or accounting consequences specific to your circumstances, obtain advice from the appropriate qualified professional.