It’s difficult to say. Some people get a lot of business from social media. For others, the benefits are a lot more indirect, offering potential customers yet another place to check out what you’ve got to offer before they contact you.
However, even if you find you don’t get much direct business from Twitter I don’t recommend going silent. You are staying at the top of people’s minds and offering impressions and touches that might lead to a phone call later, even if you can’t trace it back to your social media efforts.