I think everyone is familiar with those bins at flea markets that hold piles of unframed old prints. Often the prints have condition issues such as foxing or small tears. If, despite the damage, a print still has a really striking central image but no real monetary value that warrants having the paper repaired, creative matting can sometimes save it. A wide mat can highlight aspects of the picture that appeal to you, resulting in a dynamic new look with no need to trim the original paper. So, in essence the antique or vintage print is preserved under archival materials, but the world now sees only its best side.
In this case a mat conceals many blemishes and causes the eye to zoom in tight on the speckled botanical specimen.