This is related to but not answered in this question about the difference between various stages of a manuscript in the publication process.
After an author has submitted a manuscript to a journal for peer-review, very often the journal asks the author to revise (and resubmit) the manuscript as a precondition for its publication. I am wondering whether the term preprint refers to the manuscript before or after its authors made these revisions.
If a preprint includes revisions made in response to peer review, then there is only a slight difference, mostly regarding layout and style, between the preprint and the article that is published in the journal. From a reader’s perspective, there would be no point in paying for access to the article, since they can simply download the preprint free of charge. A publisher would probably want to prevent their authors (by publication agreements etc.) from publishing preprints that differ from the respective journal article only in form.
As a side question, what kind of preprints do publishers tolerate, as a rule?