I've worked on use cases in both work and home environments.
Remember, a few years ago, not everyone had their own computer. For large chunks of the world (demographically and geographically), this is still the case.
Shared computer? You want to be applying autocomplete=off to sensitive fields. It's no guarantee, but it's one layer, assuming other layers (e.g. preventing keyloggers) are being maintained.
Only, I guess, you won't have this option, any longer.
At one point, I had to get one of my banks (big, "evil", you've heard of them) to apply it to their login web page. And I worked for another very big corporation that had at least in some people some pretty clueful in house developers. We applied it, as well. There were, and are, valid use cases. The setting alone won't save you, but it's one piece of a broader approach.
P.S. Oh yeah, and I seem to recall nudging a domain name registrar to apply it to the credit card number field on their payments page.