I spent 15 years as a soccer referee. I wanted every call to be right, but was often not able to be in the exactly right spot to see it or just missed it. I would have loved to have help in doing the job better. Here's a situation where we don't even have to interrupt the game for instant replay in order to get the call right. Quick message into the ump's ear saying that the electronic tracker thinks it's a ball or strike, then let the ump make the call (and overrule if there is something that the electronic tracker misses). It's still a human making the call, but he has the same advantage that we have on TV.