If I remember right, the intermediate string version was already a reflection of the shifting interpreter landscape. I distinctly remember learning to always prefer Array#join for these kinds of things in 2006 or so for the same reason cited in the post.

Of course, that could have been based on a misunderstanding on the part of the person talking with me, though I would guess it matters how many intermediates (or array elements) you're talking about.

Sort of a miracle that you mostly don't need to worry about this stuff today, even running on a $100 mobile device.