I think apps have a horrible UX for browsing, but are often better than web for actual applications.
Things like Slack, JIRA, maps, Seamless - those deserve apps. And of course, games.
HN, Reddit, newspapers, even YouTube - no point in an app.
I also tend to be very picky about what apps to install because for a long time I had a 16GB iPhone and would have to delete either another app or a couples dozen photos or mp3s each time I wanted to install a new one.
I had noticed for sites like Youtube the number of people who had the app was startlingly small. Even people in my own life who downloaded tons of app often didn't have the Youtube app.
Shameful Plug: I've been working on this book site for classics,http://www.bookeyes.co/, and was thinking about whether to make an app but it doesn't seem like downloading books requires it.