Sharon Bradley (UGA) and Beth Williams (LSU) tackled this topic during the Law Repositories 2015: Shaping the Future conference. I believe I’d call their debate a draw because ultimately I think the answer to that question lies in what you are trying to preserve and/or represent with a surrogate digital item.
Digitization or conversion of analog items provides many potential benefits for items:
Preventing use (and potential destruction) of the original documents.
Providing wider access to a given item if it is uploaded to a web platform.
Providing access to individuals that are unable to travel to your physical location.
Providing access to items that may be too fragile for an individual to handle.
Providing access to items on outdated media.
But is this the definition of preservation? It really depends on the goals of your institution – and no two institutions are the same. Yes, as long as it is done correctly, digitization helps to preserve the original document because it provides access to content that doesn’t involve handling an original. However, you are creating a surrogate of an item, so it really depends on each individual researcher as to whether a digital surrogate meets their needs. To many it likely will because they care most about the intellectual content within a manuscript, letter, book, etc. However, there are researchers that will still want to see, hold, smell, etc. the original because their research interests are relevant to the physical medium.
One additional component to consider is that digitization is also not the final step in preservation. Digital formats change with regularity and just because you currently have a digital document in a preferred format doesn’t mean it will still be the preferred format a few years down the road. In order to ensure both long-term access and long-term preservation file formats will need to regularly be refreshed to the new standard/preferred format. Hand-in-hand with this is the idea of LOCKSS (Lots of Copies Keep Stuff Safe). Having a single copy of a digital file is not going to be sufficient for long-term preservation. Technology fails, files corrupt, and natural disasters strike. So it’s important to duplicate your digital content and disperse copies to ensure continued preservation. Creating digital surrogates of analog items is a component of this – in the event something happens to the original, having a digital surrogate will at least ensure access to the intellectual content.
While all of these factors are important, the true answer to this question will ultimately vary by institution. There is no single strategy to ensure long-term preservation of materials. And while digitization can be, and often is, an important component of preservation, it isn’t always the answer nor is it the final step in the process.