The apps that can take advantage of the extra speed will (video editing, batch processing, high end mobile gaming, etc).
We had practically zero CPU improvements from 2018 to 2020 iPad Pro. If Apple had kept another generation with the A12Z, even the rumored 2022 iPhone SE at $399 would be faster than the iPad Pro already.
Last year, I was testing out the 2021 iPad Pro (M1/16GB) and a refurb 2018 iPad Pro (A12X/6GB) trying to decide which to keep (both within return period). I don't know if it's thanks to the chipset or partly due to better wifi but I noticed speed improvements even in innocuous things like Mail previews loading up practically instantaneously and app updates finishing more quickly. On my favorite epub reader app, parsing my entire Dropbox account for epub files (~50,000+ epub files out of millions of files) finished much faster on the M1 than the A12X as well.
The extra RAM's pretty nice, too. While I was putting both iPads through their paces, I've never seen free RAM drop below 1GB on the 2021 Pro and I think only Disney+ reloaded (possibly intended system behavior). Meanwhile, the 2020 Pro occasionally went down to sub-100MB (before purging with accompanying Safari tab reloads).