How long do you usually keep a phone for?

Hello I'm still using my reliable Nexus 6P as my smartphone. Have been debating whether I should get a new one or not. After all, mine is 4 years old. I guess the main question I have is what can a new phone do that the Nexus 6P can't? I can text, email and watch videos. Is it worth spending money on something that may not be needed?

I'd consider at least having a backup phone handy, especially since you have a Nexus 6P. That phone was notorious for battery failure and bootloops, resulting in a successful class action lawsuit. It sounds like you've been really lucky so far, but it's always a looming possibility.

At the very least, it's time to start researching other phones. If this one is working well, then keep it. Just understand that even if the hardware remains in perfect condition, app updates often add extra features that require more resources (I.e. RAM and processor cycles) to run. Over time, you'll start to see things like increased lag and compatibility issues. That can get to the point of...

I'll be the anti-upgrader here. I have the S7, still meets my needs, I have no desire to upgrade since the improvements have been marginal not ground breaking. Like others have said, monitor battery usage, mine is not what it once was but I can still manage by paying attention to it. Until it goes up on me I'll keep it, but make sure you're backed up at all times which will make the transition...