I think that sometimes it makes sense to enforce strict limitations early on (eg: overly strict input validation). You can then remove such limitations in later versions of your software, after careful consideration and after inserting the necessary tests. The reverse usually doesn't work. If you didn't have those limitations early on, and your database is full of strings with characters that should never have been allowed in there, you will have a hard time cleaning up the mess.

This seems especially true to me in the design of programming languages. If you have useless, badly thought out features in your programming language, people will begin to rely on them, and you will never be able to get rid of them... So start with a small language, and make it strict. Grow it gradually.