This article shares some helpful advice and vocabulary for understanding how to determine digitization “resolution” based on need. It demystifies a key guideline established in many best practices and technical guidelines and explains why we sometimes do need 300ppi.
Matt Pearson, "Why 300ppi? Requirements-based methodology for determining digitization project specs" in Proc. IS&T Archiving 2011, 2011, pp 187 - 192, https://doi.org/10.2352/issn.2168-3204.2011.8.1.art00042