When true, loading keeps only this blob's bytes and Sandbox.BlobData.Deserialize(Sandbox.BlobData.Reader@) runs the first time Sandbox.BlobData.EnsureLoaded is called. For large data that is loaded far more often than it's used. Subclasses must call Sandbox.BlobData.EnsureLoaded before reading or writing their data. A blob that was never loaded saves the bytes it was loaded from.