Twitter was earlier regarded as the micro-blogging and status update tool, but right now is mainly a promotion tool for many webmasters, brands and web-based companies.
Its a great way to let a bulk load of followers know about any offers, discounts etc. only if you could manage to get a good number of followers reading your tweets/status updates. You need to have relevant people following you, for the best benefit from twitter. If you are not able to manage the following/followers number well, its waste of promoting your company there.
Twitter is also helpful as a customer service, where small doubts about your company asked by anyone, can be solved out there itself, instantly.