I've found that well-written unit tests help me narrow down problems faster during development (eg one unit test failing for a function would show that a change or refactor missed an edge case).

I've found that well-written integration tests help me catch workflow-level issues (eg something changed in a dependency that might be mocked in unit tests).

So while I think good integration tests are the best way to make sure things should ship, I see a lot of value in good unit tests for day-to-day velocity, particularly in code that's being maintained or updated instead of new code.