There is a couple of reasons for disabling automatic updates in Windows 8.1 It may be useful if you have limited Internet transfer or if an update brings new bugs instead of fixing the old ones.
Windows 8.1 comes with a feature for automatically updating programs and games you downloaded from the Windows Store. Updates to your Modern applications are downloaded without your consent. Not every user may like it.
If you have a mobile access to the Internet or you simply do not want to have your games and programs updates too often - there is a simply method for disabling these updates. You just have to go to the new Start Menu (tiles, really) and launch the Windows Store.
In this mode open your Charms bar that appears on the right (either hover with your mouse cursor or press [Windows]+[C]). Click on Change PC settings and then choose Application updates. Now you just have to move the slider, turning off automatic updates for Windows Store applications.