Having too much formal documentation and specs will box you in. Having a more unencumbered plan of development can potentially point you to where your plan was

Having too much formal documentation and specs will box you in. Having a more unencumbered plan of development can potentially point you to where your plan was lacking to begin with and tweak your idea in the process. But if you have a lot of experience with very well-defined, planned projects, by all means try to make the best of it.