Chromecast and other streaming protocols send data over your local network, but that's a problem when you're using a VPN. Those devices are looking for streaming data from phones and computers on the same network, not from a distant VPN server. Likewise, smart home devices may be gathering lots of data about you and your home that you'd rather not have intercepted. Unfortunately, these devices simply cannot run VPNs. The solution for both problems is to move the security up a level by installing a VPN on your router. This encrypts data as it leaves your safe home network for the wild web. Information sent within your network will be available, and any smart devices connected to your network will enjoy a secured connection.
If your VPN provider is based within a country that is part of the 14 Eyes, it can be asked to share data of its customers and will legally have to comply. If your provider promises that it doesn't log any information, you're probably safe within the 14 Eyes, but it is more of a risk if privacy is your main concern and you might want to consider looking for a VPN provider that is based elsewhere.
The VPN concept has been around for almost 10 years. Technologies that use public data lines for private corporate traffic promise companies a cornucopia of benefits—from saving money on expensive leased lines to a workforce empowered to access the entire wealth of corporate IT resources from any kind of connection anywhere on the globe. But as with other overhyped and overmarketed technologies, the devil is in the details.
Perfect Privacy is a 100% no logs and enforces no limits of any kind – unlimited devices and unlimited bandwidth. Their network is composed entirely of dedicated, bare-metal servers that offer fast speeds, high security, and lots of bandwidth (see real-time server bandwidth here). Like ExpressVPN, Perfect Privacy has also passed real-world tests that verified their no logging claims when one of their servers was seized in Rotterdam (customer data remained safe).
VPNs provide a way for people to get around internet roadblocks and censors, stream or download without worry, protect themselves from hackers, and keep their internet usage mostly private from third parties. They'll especially come in handy if providers like Comcast do decide to stop playing nice with Netflix, or if you're in a country where American Netflix is blocked.
If you're trying to connect to a remote media source with Kodi, a VPN would likely play a different role. It might, for example, prevent your ISP from determining what you're up to. It might also be useful if you're connecting to a third-party service for Kodi that allows streaming of copyright-infringing material. Keep in mind, however, that some VPN services specifically forbid the use of their services for copyright infringement.