While I upgrade other Apple devices (Macs, watches, iPads) much less often, I get a new iPhone every year. I’m on the auto Upgrade program, so $50/month gets me the latest and best iPhone every year (I get the Pro Max with 256GB).
Granted, the differences between new and old models has lessened over the years, but I like the camera improvements and it’s nice to not have to think or weigh the pros/cons and make a decision every year. A few times I’ve thought about skipping a year, but there isn’t much of a financial advantage (the only positive is I can own the old phone after two years and can sell it for a few hundred bucks or give it to someone who needs it).
I like never having to worry about the battery in my phone, so I charge it as often as needed and it always lasts me all day. Phones via the Upgrade program also include AppleCare, so I am covered if I break the phone or have a problem (I probably wouldn’t pay for it separately if I was buying the phone outright, but for renting it, it is required and included).
Having a new phone every year keeps me on my toes as I have to run the latest OS and move all my apps and data over – not the most fun, but at least I’m more aware of the dangers/problems than if I wait and upgrade every 3-5 years and get shocked when there are issues I wasn’t expecting (like a favorite app is no longer available on the App Store). Also, at least this way I always have a least one Apple device that’s fully modern and current, which is good for testing the ecosystem and keeping me knowledgable of the status quo.
With my Macs I tend to not upgrade them as often and I definitely don’t upgrade the OS every year, so I’m sometimes 2-3 years behind on software. But I use those for real work and want them to be stable and consistent. I tend to save my old Macs and reuse them for different purposes (i.e. media server), though I sometimes sell them to friends or relatives. That works out well as they get a good deal and my new Mac doesn’t cost me full price.
Apple Watches I upgrade when the battery isn’t lasting a day and/or Apple introduces compelling new features, so every 3-5 years.
iPads vary, as I have one that’s ten years old and still works fine and is just used for reading ebooks at night, and one that’s a newer M1 device I use during the day and for traveling. (I recently bought a “kitchen” iPad that is also used for guests who want to check their email or whatever. I was tempted by Apple’s latest, but ended up getting a cheap $200 two-year-old model from the Apple refurb store that does all I need and had twice the storage of the old one I had which was sluggish and running out of space for even basic apps.)
I like my strategy, but I realize it’s not for everyone. I kinda wish Apple had an annual Upgrade program for Macs. I might consider that, depending on the cost.