Advice on setup and common misunderstandings

I'm extremely new to self-hosting and wanted a setup with emphasis on privacy and security.

At the moment, I'm deploying Nextcloud and Vaultwarden in my Docker containers.

Both are only accessible over Tailscale or LAN. I was wondering, what is the advantage of opening ports or reverse proxying? Like why do people host public rather than fully private for their stack?

I am probably misunderstanding something so feel free to educate me in the comments.