If it was instant we wouldn’t have latency and the three generals problem would be somewhat trivial (ordering would be mildly interesting in an algorithmic sense, but practically meaningless).

we were hungry so we decided to discuss this philosophically over a pasta lunch, but we deadlocked with our forks and that dispute kept us from our main topic

For most use cases that's true. But for a surprisingly large number of use cases that's not true at all.

I was thinking of using a high-frequency trading example, but here's a case that's a bit more normal: stadium concert audio for a live band. Stadiums are big enough that you need to deal with latency issues for audio, because the back of the venue will get its audio a bit later than the front of the venue (assuming the sound is wired so the board is in the front of the floor and no adjustments are made). That is obviously disconcerting to the audience. Adjustments usually are made to handle this problem.