Twitter if used properly can be utilised for marketing and excellent results can be obtained too.
Twitter is web 2.0 site and has recently gained huge popularity due to its simplicity and ease to use.
Twitter marketers try to gain as much followers as possible as more the followers you have the more exposure your tweet oe messge will actually get.
Just think you want to promote an affiliate product and with twitter you can pass on your message with affiliate link to all your followers so like you have 1000 followers then you can instantly send your message to all of them free of cost.
This is called as effective free of cost twitter marketing.