A double-blind peer review means that both authors and reviewers do not have access to identities and affiliations of each other. In the single-blind case, the reputation of authors MAY affect the comments of referees, or it may be a source of probable conflict of interest.
My experience in reviewing more than 170 manuscripts for more than 53 journals in the field of mechanics, physics, and mathematics unfortunately says that most journals in my field are sending the manuscripts to the reviewers including the names and affiliations of authors inside the file.
Please don't mention that the referees need to know the identity of authors to find possible overlaps with their previous publications. Please share your answers after my question. Maybe we can send a clear message to journals in our field to change their unfair procedure.