In addition, it is also easier to search chats in case you forgot something that was a few years ago (party, prom, etc.)
In principle, chats do not take up much storage space, they are plain text (encrypted once saved / backed up). Definitely the biggest concern in terms of storage is the photos and videos being sent/received.
This is why it is best to keep an eye on chats occasionally and delete unnecessary chats.

It happened to me that when Whatsapp did not save backups to Google Drive, my phone fell out of my hand and the screen broke. The repair was more expensive than the new one, but the only backup I had was local…
Since the online backup was released, I’ve been running the backup daily for both my parents and me.

I’m curious how much space the backups take up and if some compression isn’t done. In addition, I rarely use Google Drive, so Whatsapp can use some of its space.

Storage in any form costs money and not everyone benefits fully, so it is better in terms of efficiency to reduce unused storage. Who knows, there might be an option for thin provisioning, you’re only using actual storage and not reserved storage.