For me it's mostly for the lulz because Samsung is the first device I have owned that can actually record calls. Secondly it helps to listen in case you missed out on some information or you need clarity.
Same for me. It helps to listen recording again to understand some points (particulary job related calls). Although I may be listening 1-2% recordings only again. I delete most of them occassionally without listening
Even if you have Google phone app, call recording needs to be enabled from Google's server side.
In my case, Poco X3, it was not enabled on the app. After much pursuit from Xiaomi, users did google enable it.
I think they are enabling it but slowly.