Great question!
In a nutshell, the Web Application is where all projects are created and managed through their life-cycle. The native iOS and Windows apps on the other hand, are built for mobility and is where the natural pen-like markups are possible.
The Web Application is accessible to anyone on the project through any modern web browsers on almost any device. As all key project administration tasks are performed through the Web Application, the app is designed to be accessed on a desktop or laptop with all key information clearly visible or easily accessible at all times.
Web Application:
Once your projects are set up in the Web Application, it is strongly recommended you download either Windows 10 App or the iOS App to view and mark-up your project documents with the very best pen and touch technology.
Windows 10 Application:
Unlike the Web Application, the Windows 10 App and iOS App both include offline functionality to ensure users can continue to view and markup their documents without a network connection.