What ECMAScript 5 'use strict' string costs exist?

Question

What is meant by 'use strict' string costs in almond.js line 6?

A Google returns no information on the issue the author seems to be implying.

Answer 1

And the answer is apparently:

It is extra bytes to deliver the 'use strict' string in the source, and this is trying to be a small library. So, just a way to reduce file size by a little bit.

Which is a pretty silly "cost". It's 13 bytes before compression -- that's insignificant.