Are Deadlines Hurtful or Helpful to the Writing Process?

I have always been in the belief that goals are important, keeping a person focused on what needs to be done and usually giving a time-frame for when said project needs to be completed. It keeps us from running around in circles and gives us purpose. In a sense deadlines are the same, but on a smaller scale. Deadlines are usually for very specific projects and have a definite timeline. It’s a strict date to work towards and a feeling of doom if said project is not completed by the expected date. Deadlines too can be helpful in motivating a procrastinating body (such as myself) to keep moving forward and having a sense of accomplishment from completed deadlines, but what if this strict process creates a pressure that stifles the creative spark?