I've used FIM in the past to catch a CEO modifying files in real-time at a small business so I could ping him and ask him to kindly stop. It's not just about BS _processes_. :D
That means CEO has access to do the changes. It's technically easier to remove that, than to insert FIM into the deployment process. (And will stop other unauthorised employees too) I mean, you already need a working deployment pipeline for FIM anyway, so enforce that?
The CEO would've found it very easy to remove the blocker in that case (me). This is the life of small tech businesses. Also, they were modifying configuration files (php-fpm configurations iirc) and not code.
FIM is very useful for catching things like folks mucking about with users/groups because you typically watch things like /etc/shadow and /etc/passwd, or new directories created under /home, or contents of /var/spool/mail to find out if you're suddenly spamming everyone.
That’s a great real-world story. Exactly the kind of unexpected modification FIM can help surface—not only security incidents, but also operational surprises.