As formats change and the media they're recorded on ages, it becomes increasingly difficult to transfer the information off of those formats into new, more modern formats. That's basically what archival and restoration is: transferring recordings from one format to another. Usually, the transfer is from an older format on more fragile media to something newer and easier to work with.
Layback Mastering is the process of recording your mix to analog tape and mastering from the analog tapes. If you recorded and mixed completely digitally, you may consider asking about tape layback as an option for mastering. It can add that analog 'warmth' to a project or give that last little bit of 'glue' that makes a mix really come together. We have several choices in analog tape machines including Ampex, Sony and Studer. Each sound a little different and each has different options.