The cost of retyping between systems
Almost every business over a certain size has somebody whose job includes copying data from one screen into another. It is slow, it is error-prone, and it is almost always cheaper to fix than to keep paying for.
Integration work is unglamorous and unforgiving: the interesting part is not the happy path but what happens when the other system is down, returns something unexpected, or silently changes its format. We build for that, and we make failures visible instead of letting them queue up quietly.