One other reason to setup back-ups immediately and (performance) monitoring as soon as possible has to do with another phenomena: When a new version is released under time pressure, things are more likely to go wrong or cause trouble because testing in a production-like environment is usualy very time consuming.

Even without any problematic changes in the database itself, changes are bigger that a piece of newly developed or sligtly adjusted code will have a dramatic impact on query performance, cause deadlocks or corrupts the data in ways that could have been avoided with proper constraints if there had have been more time to implement and test them thoroughly.

One last additional advice: NEVER forget to back-up the database BEFORE you deploy a new version of the software. No matter how much you are in a hurry, you will always regret it when you can not restore the previous version. Too often it is needed when something goes wrong, just to make a side-by-side comparison, or to rerun the upgrade scripts when it gets stuck because some 'small' changes were made by hand in the test environment.

See you at the next upgrade!