It's often recommended that you should use a VPN when using unsecured or untrusted networks, such as open public wifi or secured wifi that you don't control. What are the advantages to using a VPN on any network (wifi or wired), even a network you own/control?
If you control the network, there really isn't an advantage (under almost any circumstances). What a VPN does is simulate having a leased line from your computer to the network the VPN server is on. If you are already on that network, there is literally no advantage (unless you enjoy encryption overhead).
There is one main exception: if you control the network, but you cannot fully trust it, and the VPN server is on a separate network you can trust. For instance, if at a school you're worried people might tap into the cables somewhere on campus, but the VPN server and the routers to the Internet are all physically secured, you might not trust the campus network. Likewise, my guess is that ISPs have intranets that are separate from their networks they sell to clients, and that an ISP engineer might VPN from the ISP network even though it's the network they control.
It's important to note that using a VPN just means you're virtually on the network of the VPN server. If it is better to be on its network than the one you are physically on, you should use a VPN (for instance, if there's intranet stuff you need to access). For security purposes, you should use a VPN if and only if you trust the VPN server's network more than your own; it provides absolutely zero security past the VPN server; the only part of your communications that is secure is the path from the local network to the VPN server. If you're using some VPN provider that you trust more than your ISP (not necessarily a good idea, incidentally), then it can give advantages. If you're not worried about someone tapping the local network and you don't trust the VPN provider (and their ISP) more than you trust your network (and your ISP), it's stupid to use a VPN.
The advantages of using a VPN is that content you access on the internet and anything sent to a website is encrypted and routed through vpn. When a connection is encrypted it stops people from monitoring your connection. So all data send to website can't be read by anyone except the VPN provider. When a connection is not encrypted a attacker could preforming a mitm(Man in the middle attack) where the attacker can view all data that is not encrypted that you send to the website including usernames and passwords.