Having a lack of confidence can lead one to being used. It can also prevent you from expressing yourself in many ways.
During my years at Music College, I lacked confidence and felt it was affecting my performance on stage. I developed a method for boosting my confidence which to begin with, I found quite challenging.
On my avatar, you can see I am wearing a wizard hat (and starry sunglasses and an awesome guitar ^^). I wore this hat to college every day for an entire year. This included wearing it on the bus, to any event I went to, and even when I went to town for food with friends.
As the hat is so large, it meant that I was noticed wherever I went. This led to practically everyone staring at me all the time. I felt incredibly uncomfortable with it to begin with. As the days went on however, I began to get used to the feeling and my confidence began to grow.
Some did not take kindly to the hat though. In fact a massive argument started because this one guy thought I thought I was above everyone. This escalated to the point where he was unfortunately expelled.
My level of confidence is much higher now because of that experiment and I am happier for it.
I would say it would be better to have confidence in expressing yourself than not.
Although, confidence is sometimes confused with arrogance.