Live performances are a great way for you to promote yourself. They allow you to get face to face with your fans, and make new fans along the way. They’re also great for selling your material, as even if the audience hasn’t heard of you before, a good performance could turn them into a life long fan and customer. This applies especially to showcase events and to a slightly lesser extent open mike nights, as the people attending these are usually music fans that are used to buying CDs of anyone they find interesting.
Scouts for record labels and music competitions among other useful industry link also attend live performances and showcases, so doing a lot of shows will surely put you in contact with people that could help your carer in the long run. Some shows are also video recorded, so your performance may end up online, on TV, or on DVDs.