In the previous version in definitions/storage
You be able to see the tab /cache and the only option you have when touch was clear cache. I think that option clear all apps cache. Always I perform that action for release space to update Gapps.
Now to do that I need definitions/apps/storage and then clear cache in every single app
I think that Oreo cleans the stored cache of the apps automatically after a certain quota is reached so that's why the option to generally clean it has been removed. You can still clean it manually for every individual app if you want or need to.
Someone correct me if I'm wrong.
That is only for downloaded files and less use apps.
For example, I use Facebook app today, and Facebook app use a lot cache files and because of that I already see the notification less space on device for 4 or 5 times today.
The SO clean automatically and the notification disappear, but in the previous version I wasn't that problem because I clear the cache periodically