Why use an additional VPN (to prevent against snooping) if https is already encrypted? Is it solely for an additional layer so snoopers need to decode the data twice?
HTTPS encrypts the content but:
Anyone watching the stream, including your ISP, can easily see that you are going to www.bluebuggybumpers.com, or my.aids.results.com, or what have you. A VPN blinds your local ISP to where you go, although the VPN is capable of the same monitoring.
The site you visit directly see's your IP address and can generally instantly know within a sub-city locale where you are located. With additional assistance from your ISP, they can locate your specific internet connection. A VPN presents the VPN's IP address instead of yours.
Your geographic locale, determined from your IP address, may result in restrictions along the lines of Dr. Who is UK Only, or blocking North Korea. A VPN can be used to appear from almost anywhere in the world.
Some ISP's block certain protocols like bittorrent. A VPN allows you to run blocked protocols.