I don't use a VPN, and it's because the answer to that question is "none".
(I'm using the term "VPN" to mean "proxy with a nice name", like NordVPN, not an actual VPN set up for e.g. being able to access your home NAS from the internet)
There, I said it. Using a VPN won't protect you from anything in any way.
Almost all traffic from and to your machine is already encrypted (HTTPS) and the stuff that isn't (like DNS) is a matter of privacy, not security.
Privacy-wise, using a VPN will hide that tiny remaining bit of data you might be leaking (like DNS, essentially "websites you're looking at", not specific pages, just hosts like facebook.com or youtube.com) and then expose all that somewhere else, where your ISP can't see it, but everyone else can, including your VPN provider, any router on the way from the VPN provider to the DNS server and the DNS server itself.
Please note that the VPN provider sees the exact same traffic as the malicious coffee shop owner whose WiFi you're on would see if you weren't using a VPN, i.e. huge chunks of encrypted traffic to visible and readable IP addresses.
Now this part might be important, because hiding stuff from your ISP is a legitimate concern in countries like China or Russia, or if you're forced to use an ISP who's a piece of crap and will try to block or throttle certain types of traffic (traffic to IPs known to belong to Netflix or torrent trackers etc.).
This is where using a VPN service makes sense, if you're really really really concerned about privacy and you trust your VPN provider more than your ISP or country (it sounds ridiculous because it is).
At the same time, using a VPN won't stop Google or Facebook following you all around the web, because Google and Facebook don't give a damn about your IP address, they use much smarter techniques like browser fingerprinting, tracking cookies and having their tracking Javascript on almost all websites you ever visit.
tl;dr "VPN" services like NordVPN are useless security theatre unless what you want is watching unavailable movies on Netflix.