It may only be to your benefit to register your business is you buys large quantities of goods from suppliers, which would entitle you to claim back the VAT you pay.
Keep in mind that you would have to increase your prices by adding VAT, which could make you more expensive than your competitors.
You must also consider the fact that being a vendor would result in in additional administration and possible cost in that you would required to keep proper accounting records to submit returns to SARS on a regular basis.