In their tests with the 256 GB iPhone 7 Plus, the phone that they used had 75.45 GB of storage remaining. However following the update to iOS 10.3, it was later discovered that they now had 83.26 GB free, meaning that the update and presumably changes to the new file system resulted in the freeing up of 7.81 GB of storage. Of course your mileage might vary but basically it seems that the shift to APFS has resulted in more storage for users.
Now obviously this doesn’t mean that you’ll be able to get away with purchasing a 32 GB iPhone model since you’ll be kind of pushing the limits, but we guess in the long term you should be able to get more out of your storage than you did before. It is expected that developers will also take advantage of this to make their apps more storage-friendly in the future.
If you’d like a more detail breakdown of what APFS is or what this means for iOS devices, you can head on over to AppleInsider’s website for the details.