When I started my job as an intern, I was surprised to learn that before each release, the techlead of our team would always manually verify every commit in the release branch to make sure that the issues in the issue tracker that correspond to the commits are actually marked as "to be merged" and greenlit by QA, that there's no commits accidentally merged from other branches which aren't ready for a release yet (juniors often mismerge by accident), he also checked that all commits from the original feature branches were merged and none were missed (happens sometimes) etc. It would take him 1-2 hours to sift through all commits every time (each release would incorporate tons of features/fixes and commits weren't squashed, so there was a ton of work). The techlead also didn't allow anyone to do this work because he feared people wouldn't be as attentive as him. I remember there was one time when it was 11 PM and he was still verifying the commits and the release managers had to wait and couldn't go home.

I wrote a script which finds new commits not present in the master branch and compares them to the corresponding issues in the issue tracker (each commit message has an issue ID as a rule so it's easy to find the connections), and then generates a nice report like "the release branch cannot be released as is because issue 1234 is not marked as ready by QA, while commit 3456 is not present in any of the listed feature branches and could be a result of an accidental merge".

After we started using this script, the time it took to verify release branches decreased to something like 10 minutes. The techlead finally decided to delegate this kind of check to other devs (not a bottleneck anymore).

The idea was then copied by all other teams (web devs, etc.) and the script is still in use today, with many more features than I originally envisioned.

That small silly script was probably my most useful contribution because it saved a lot of time for everyone.