After school I did an IT support role for a further education college. They used to spend most of the summer formatting the machines, reinstalling Windows, off

After school I did an IT support role for a further education college. They used to spend most of the summer formatting the machines, reinstalling Windows, office, anti-virus etc, doing them manually a classroom at a time. We replaced it with a system of hidden partitions and a disk image, then the ability to trigger a refresh remotely if pre-requisites were met. This is common practice nowadays, but it was quite innovative at the time, and we had to write a lot of the code ourselves for remote admin and to make the disk refresh reliably. We could then click a button and refresh ~500 machines in the space of an hour as opposed to 6 weeks of manual labour. I've worked on more prestigious stuff, but that was the most satisfying and the most obvious avoidance of manual efforts.