Some practical benefits are

• Much friendlier/intuitive installation process (compared to web app)
• The app can register itself into "Share" dialog, so e.g. you see some good article in any app, click on share, SN is an option to immediately create a post out of it
• Easier to do the views and animations (it's possible with web app, but somewhat tricky to make it performant)
• Good notifications when you earn sats, or a person you are following posted something (again can be done with web app, but it's not that easy)
• The post detail view can have two tabs - one to see comments and one to see the actual iframe. That would make it really easy to go back and forth between the article and comments.
• Thumb friendly UI - e.g. the common actions are on the bottom so those can be reached by thumb. Also "tap" targets would be bigger...
• Standardized/intuitive experience, e.g. hamburger menu in the usual place as in other mobile apps, etc. When you you swipe the left sidebar shows up.
• Potentially can act as a mobile wallet (this is more of a brainstorm, but it would be cool to earn some sats on Stacker News and buy a beer with that immediately...)
• Idea: Could have a "Read later" feature to essentially create a backlog of articles that I would like to read when I have time...

I also like the web app and it should always be an option to use web app, but there are some practical benefits to mobile app.

@k00b