"There's a lot of drama around deployments because they aren't fully tested."
Not to mention that they might not even have been fully thought-through.
I have the feeling these days that sysadmins do not have the time to project and plan, they have to put out fires all the time because management pushes things through that always have to be done yesterday.
The IT department that has a comprehensive list of all applications, servers and functionalities, up to date and with dependencies, probably doesn't exist.
As such, when it is time to deploy something, the approach is very much "do it and see what breaks". Oh sure, they'll have had meetings and they'll have defined what the end result needs to be, but nobody will have listed everything that can break and what needs to be done beforehand to avoid the issue.
Just recently I was at a site that had just deployed a new domain for a company that had been acquired. I was called in to help re-stitch the relevant links in their applications. It was a process of check, control, correct. Meaning that I had to go through all the apps I knew of in their existing domain, and check that the configurations and code were properly modified to include the new domain and function with it.
I was not given a checklist, nor was I aware that they knew what needed to be fixed. Thankfully, I knew what apps I was in charge of there, and I also knew a bit about a few others, so things were under control rather quickly.
I can't say that things were very well planned, though.