Microsoft Windows 10 Update Assistant is designed to prepare your computer for upgrading or updating Windows 10 by checking for compatibility issues and downloading all necessary files to start the install.
While Microsoft Windows 10 Update Assistant can check your computer to see if it can run Windows 10.
Beyond that, Windows 10 Update Assistant is geared towards advanced users and IT departments looking to get the latest large updates, for example, the Fall Creators Update.
In other words, Microsoft Windows 10 Update Assistant can download updates that are available but not in your Windows Updates yet. Everyone will eventually get the updates through Windows Updates.