This has come up so many times on this very subreddit. If you just search it, you’ll see a monthly thread where this is discussed and link to Apples white paper detailing how caching works.

I’m not sure why people are so hung up in system data usage. In iOS, any surplus free space can be used as a swap or chache. It will be available if you have more data to write on device. In no way is all of that space locked up. Any space you “free up” using OP’s method was always available on your device whenever it was needed.