In this case... pretty meaningless honestly.
Binning is separating CPUs, GPUs, whatever, based on capabilities or defects. If you have a CPU where one core doesn't work, instead of chucking it away, you sell it as a lower-end chip. If you have a CPU that doesn't work when clocked at full speed, you don't chuck it away, you sell it as a lower-end chip. Sometimes when too many high-end chips work just fine, they're artificially turned off in software, or a fuse burned in hardware, to create more lower-end inventory. This is how GPUs and CPUs have been sold for decades.
When people talk about a binned chip it's not terribly clear what they mean as every chip is binned, it's a matter of which bin they end up in. It's like sorting your Legos by color. They're all sorted into bins, piles, or whatever. You don't say the yellow ones are not binned. Usually though, when people mention binning they intend it to be a negative, and mean it's a lower-end variant. That was the intent here, but...
According to Apple, both the iPhone 14 and SE 3 have a 6 core CPU (2 performance, 4 efficiency), but the iPhone 14 has a 5 core GPU, while the SE3 has a 4 core GPU... on the other hand the SE 3 has got only 34% of the pixels, so it's actually got more power per pixel than the iPhone 14. It's not really going to make much of a difference, and may very well be in the SE 3's favor in non-benchmark use.
Sure, get the iPhone 14 for the clearer screen, larger battery, better camera, something meaningful... but due to binning? In this case the numbers say that's just silly. Anyway, anyone considering an SE 3 was looking for a small phone, so you'd be considering the 13 mini, not the 14... and wouldn't you know it, it has the same A15 2P, 4E, 4GPU cores as the SE 3. Yes, again, it has a better screen and camera, but it cost significantly more.
You don't need the best in class of everything, especially if it's worse for you. If you use your phone rarely, and want something small, like me, the SE 3 is fine. If you're on your phone all day, then yes, it makes sense to invest more in a better phone. If you need small, get a mini. If you want big, get a regular. If you want extra large, get a Pro or a Pro Max. They make different models to suit different needs.