Short answer: not always, but more often than the marketing makes you think, and usually for different reasons than the ads give.
A VPN does two specific things. It encrypts the traffic leaving your phone, so whoever runs the network you're on can't read it. And it swaps your real IP address for the VPN server's, so the sites and apps you use see that address instead of yours. That's the whole product. Everything else follows from those two facts.
So the honest way to decide is to ask where your phone actually connects, and who you're trying to keep out.
When a VPN genuinely helps
On Wi-Fi you don't control. Coffee shops, hotels, airports, a friend's flat. You have no idea how that router is set up or who else is on it. Most websites use HTTPS now, which already encrypts a lot, but not everything leaks equally. The names of the sites you visit, some app traffic, and anything still served over plain HTTP can be read by someone on the same network who's paying attention. A VPN closes that gap.
When you don't want your IP tied to your activity. Your IP address is roughly a postcode for your connection. Advertisers and data brokers use it to build a picture of you over time. A VPN breaks the simplest version of that link.
When a network is blocking things. Some hotel and office networks throttle or block services. Routing through a VPN often gets around that.
When it does less than you'd hope
A VPN doesn't make you anonymous. If you log into your own accounts, you're still you. It won't stop a website tracking you with cookies once you're signed in, and it won't protect you from a dodgy app you installed yourself. It also can't fix a phone that's already compromised. Treat it as one layer, not a force field.
If someone sells you a VPN as total invisibility, they're overselling it.
What about on your home network?
At home you control the router, so the public Wi-Fi argument mostly disappears. The reason to run one at home is narrower. Maybe you don't want your internet provider logging every domain you visit, or you want your IP hidden from the services you use. Both are reasonable, but they're optional. Be honest with yourself about which you actually care about.
The thing that matters most: who runs it
Here's the catch people miss. A VPN moves the trust, it doesn't remove it. Instead of trusting the coffee shop's router, you're now trusting whoever runs the VPN, because all your traffic flows through them. A free VPN that quietly sells your data is worse than no VPN at all.
So the questions worth asking before you pick one are short. Does it keep logs of what you do? You want a clear no. How does it make money? If you're not paying, you're usually the product. And does it cover every device you own, not just your phone?
That last one trips people up. Your phone isn't the only thing leaking. Your laptop and tablet do too, often on the same untrusted networks.
A simple rule
If you regularly use networks you don't own, a VPN is worth it. If you only ever connect to your own home Wi-Fi and you don't mind your provider seeing the domains you visit, it's a nice-to-have rather than a must.
We built DeviceDecoded VPN for the first group. One subscription covers your phone, laptop and tablet, there are no activity logs, and it's a flat $10 a month with no contract. It's the same approach we take with the rest of our device tools: tell you plainly what something does, then let you decide.
And if you're setting up a phone you bought second-hand, privacy starts before the VPN. Run a quick IMEI check first, so you actually know the history of the device you're about to trust with your accounts.