I disagree, because the scope doesn't escape those functions and it can greatly reduce the amount of :: Usually in an entire codebase or a module there's a lot

I disagree, because the scope doesn't escape those functions and it can greatly reduce the amount of :: Usually in an entire codebase or a module there's a lot of competing, similar symbols. But in a function that's not the case, because they do something small. So there's no benefit to being more "explicit", because the function already states what it does. For example you might not want to use std::chrono. But in, say, a series of timing functions you really don't want to be writing std::chrono:monotonic_clock::now(), do you? You can just use a using and then just call now() or whatever.