The storage question is the one with the most expensive mistakes when buying a phone: too little storage means years of deleting and juggling, too much means paying for gigabytes that never get filled. And on iPhones and most Android flagships, nothing can be upgraded later. Here is the honest decision guide.
Check how much you actually use on your current device: on iPhone under Settings, General, iPhone Storage, on Android under Settings, Storage. That value plus 30 to 50 percent headroom is your target size. Data grows, but rarely in leaps.
If you stream music and films, back up photos to the cloud and use the usual apps, 128 GB will comfortably see you through. That's the value-for-money recommendation for everyday users, parents' phones and second devices. Just be careful if you film a lot: 4K video fills 128 GB surprisingly fast.
You prefer keeping photos and videos locally instead of in the cloud, film the kids in 4K or install big games? Then 256 GB is the relaxed choice, enough headroom for several years without storage stress. It's also the right size for mobile work with offline files.
Huge video projects, complete offline media libraries, professional workflows: only then is the top shelf worth it. For everyone else, the surcharge is better invested in a higher condition grade or a better model.
When buying new, storage upgrades are traditionally overpriced. Refurbished shrinks this surcharge considerably: the jump to 256 GB often costs only a little more used, because the price follows market value rather than manufacturer list prices. So it's worth comparing both variants in the shop, sometimes the bigger model is even cheaper, depending on condition and availability.
iCloud and Google Photos offload photos and videos and take huge pressure off device storage, in exchange for a monthly subscription. Do the honest maths: if you permanently need a large cloud subscription, paying once for more device storage often works out cheaper.
128 GB for streamers and pragmatists, 256 GB for photo and video collectors, 512 GB only with a concrete reason. Check your real usage, add some headroom, and use the small storage surcharge on refurbished devices to your advantage.