Each MOBILedit software update consists of new features. Package updates consist of data, which are important or necessary for those features to work properly. For example, to use the Face matcher feature, you need to update the Face matcher package.
MOBILedit allows you to update packages related to individual features that were released or enhanced after the release of the newest update. Updating individual packages will allow you to get the latest version of a feature that you might need for your investigation.
MOBILedit will work even without updating a single package, however, an important analysis might be missing without updating it.