No, not Google+ the failed social media service. I want to talk about the + operator that Google Search used to support.
And, my memory not withstanding it appears that intent and meaning of + in search changed over time.
I remember believing it prevented optionality for more than common words. I can't recall exactly when I believed this or if I ever knew it had changed to a verbatim meaning, but quotes always seemed the more natural symbol for the latter. I'm sure my belief in the obligatory-but-not-verbatim meaning of '+' was supported by its apparent contrast to '-', which excluded search results with that term, since it makes sense that the opposing symbols would have opposing meanings.