Nobody needs an app for anything, but the Reddit app is far superior for me vs. their mobile experience. So much so that I refuse to install it because it makes Reddit far more addictive. Same for Facebook. A huge percentage of their usage is the mobile app vs. mobile web. Like Reddit, part of that is due to them making the mobile web experience crappier to drive app adoption, but that's not the only thing going on. The web just for UX in many ways, and will never beat a well-built app for anything other than ease of initial installation.