The iPhone 7 comes in three different storage sizes, and in theory, the only difference between the three is size. But as it happens, the 32GB model is much slower than the bigger models at a number of real-world tasks.

We’d already heard from GSM Arena that there’s a difference in the quality of storage, and a new video from Unbox Therapy‘s Lew Hilsenteger explains the difference, and how it might affect you.

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Hilsenteger begins by testing the 32GB iPhone 7 against the 128GB model in disk benchmarks. Using PerformanceTest Mobile, he tested the read and write speeds of the storage in both phones. While the read speed is the same, around 700MB per second, the write speed is much worse on the 32GB model. Specifically, the 128GB model writes files at a speed of 341MB per second, and the 32GB goes at a much slower 42MB per second.

Disc speed can make a big difference in real-world performance, especially on the iPhone. iOS is more prone to push apps out of the RAM and store data on the disc drive, so the longer it takes to read and write files, the slow the phone will perform.

More noticeably, tasks like copying movies from a PC to a phone will take much longer on the 32GB model. I know that you probably don’t copy movies across from iTunes all that often, but more mundane things like copying photos — or restoring your phone from a backup — will still take longer.

Aside from the speed issues, there’s also the fact that buying the 32GB iPhone is a bad move. Sure, it’s better than the 16GB of storage you used to get with an entry-level iPhone, but it’s still not enough. Add in things like photos shot in the RAW file format, which can be as big as 15MB on the iPhone 7, and you’ll quickly eat through that much storage in a few months. The 128GB option is much better for general use, and you’ll probably forget that there’s an upper limit on your storage at all.