A VPN encrypts all of your outgoing communication and as a result offers total protection from hackers, snoopers and government agencies. It is unfortunately widely underestimated how unsafe and un-secure Public Wifi networks are, and by connecting to one, a half decent hacker can monitor any output from your device; this includes passwords, emails, bank details and social security numbers etc. A VPN totally mitigates this risk and uses secure protocols to encrypt traffic from your device.
If you are doing anything other than general browsing i.e reading the news, you should certainly be using a VPN.
In addition to the huge security benefits of a VPN, it can also circumvent geo-restricted websites, hide you IP from the outside world and prevent your ISP from throttling your bandwidth.