The white border of a mat board is of a different reflectance (duller) than the white border of photo paper. It is my opinion that the white border of photo paper around a print is distracting.
I dry mount l of my prints, so there is not a black border, nor the white border of photo paper. According to testing that was done comparing dry mounted and hinged prints it was found that the dry mount tissue provided a significant benefit regarding archival longevity of the print.
Michael A. Smith