I'm not saying they're not useful, pinterest is hardly a giant in my opinion, they do one thing and clearly do it well. I'm sure their position on unit tests will change, hopefully before they are burned.
It is not impossible to have a large code base without unit tests. I'm sure my employer's code base is in the millions of LOC. At least 99% is not covered by unit tests. Probably 99.9%.
That might work for you, but is a bad idea in 99% of cases (I am not implying that most code has tests in place). I guess your code changes very rarely.
If you have to change something in core part of application with a lot of dependencies, good luck. Also, when several programmers are working on the same part of code (perhaps in a span of 5-6 years), they will need some time to understand code to be changed, then think more where something might break if they change it. At the end, they will lose a lot time and still not catch all the interactions with other code.
It took me a lot of time to understand why people want to write tests first, then code. It was more natural for me to make optimal code, then test expected/unexpected inputs and edge cases. The answer turned out to be that code ends up much cleaner and all code paths end up tested properly because you never write a single line of code which isn't explicitly there to satisfy a test.
