Joyce is correct. A domain name makes your business more secure in the long term because you're not tied to somebody else's domain name - they could go bust through no fault of your own, leaving you with the prospect of starting your promotion campaign all over again, from scratch.
It also gives you prestige in the eyes of potential customers. A domain name shows that you're serious about your business.
You still need to put the same amount of effort into your promotion etc. a domain name isn't a magic formula.