Popcorn time and VPN are two things that cannot be separated. They are or they should be used together to stay safe. Popcorn time is an app that most people use to stream those movies that are only available at some other streaming application or have some copyrights that are not with Popcorn.
This is something that can put them in a lot of trouble if the ISP reports the activity, the producers and film fraternity can file a case against them.
There are movies and shows that can be watched without using a VPN on Popcorn Time but most of the people desire to watch the content that is not legal to watch on this application. So this is where the VPN use comes.