Actually, Wordsworth has said that it can be freeing to have to follow a strict format. If you choose to be in a "prison", it's not a prison any more, is it? If you are so free that you have to decide everything, you are imprisoned by the weight of too many things to choose from.

  That's actually not how I feel about it. The reason why I write formatted poetry is because... I want to. It feels good. It feels musical. It's quite rhythmic. Not that I only write formatted poetry. I only write it when I want to. That way, I can be sure that the format is actually a part of my expression, and not just a constriction to stick myself in.
  When it's really a part of the piece, it adds meaning. Some rhythms are hoppy (yes, hoppy), and make a poem seem brighter. Stuff like that.