Well, actually, there is not much more to say about this than what is in the title.
Of course, the main advantage of being able to use single-quote strings is when your string contains various double-quotes. So, you know, for example, Java has (since JDK 14 or thereabouts) a multiline string which starts/ends with 3 double-quote characters, so before, you had to write:
"\"\"\""
(blah blah blah)
"\"\"\""
Now, this can be specified as:
'"""'
(blah blah blah)
'"""'
since, when using double-quotes inside the single-quote string, they don't need to be escaped. (Though they can be if you want!)
Of course, one can now write three 3 single-quote characters as:
'\'\'\''
but that would be a tad perverse. I guess most people would continue to write:
"'''"
And, then, aside from that, it's just an aesthetic choice, I suppose. I was pondering the usefulness of there being some semantic difference between putting a string in single as opposed to double quotes, but in the context of the regexp spec, I couldn't see anything much to do with it. So (at least for now) it just boils down to not having to escape the double-quote character because you can enclose it in single-quotes and conversely, of course, you don't have to escape the single-quote, but that was already the case!
Well, this kind of thing is so marginal really, but I think every little improvement like this, incremental as it may be, as in this case, over time, there is a cumulative effect and the tool just becomes much nicer to use.
I'm also working on some other things that will be of much more fundamental importance, but I figured I'd just take an hour or so and pick this piece of low-hanging fruit.