The article is interesting, but it is frustrating that it mainly cares about speed, but 'speed' or 'fast' is not mentioned in the title.

To answer that general title question, I would not even have considered that 'speed' might be an issue. I'd say: pass small things by value because it probably results in the most readable code, which should always be the first dimension of optimisation, I think. Also, the compiler is most probably good enough anyway, so care about your source code readability first.

So, at least the title should say 'if you care about speed a lot'.