In my personal opinion, the reasons for using it don't outweigh the reasons against it, but either way, the reasons for using it ( / an app store in general) are:
1) Convenience:
You don't have to search all over the web for your software and don't have to click through an installer when installing (because everything is packaged in a standardized way and can therefore be installed in a standardized way, too). Also, there's a centralized way of distributing updates now, meaning that not anymore each and every piece of software has to come with an auto-updater.
2) Security:
If you don't install your stuff from the internet, you're also much less likely to install from a wrong source and therefore less likely to catch viruses. If there is a virus-infected app on the Windows Store, it's also possible for Microsoft to remove it. The UWP-apps that Microsoft is pushing along with their store, are also sandboxed, so again, much less likely for software to be able to damage your system.
For what? Everything is available on the Internet. I have used Windows 8, 8.1 and 10 for years now and I have never felt the need to install anything from the Store.
1) Convenience: You don't have to search all over the web for your software and don't have to click through an installer when installing (because everything is packaged in a standardized way and can therefore be installed in a standardized way, too). Also, there's a centralized way of distributing updates now, meaning that not anymore each and every piece of software has to come with an auto-updater.
2) Security: If you don't install your stuff from the internet, you're also much less likely to install from a wrong source and therefore less likely to catch viruses. If there is a virus-infected app on the Windows Store, it's also possible for Microsoft to remove it. The UWP-apps that Microsoft is pushing along with their store, are also sandboxed, so again, much less likely for software to be able to damage your system.