Firewalls, absolute nessecity or a nuisance?

I’ve been thinking about this in regard to another topic regarding cloud storage. Suppose you host your own cloud. Would it be wise to have a firewall?
If so, what would that have to be? Hardware or software? (Like ufw?)
I’m new to the world of firewalls, hence my question.

most people dont use firewalls, and rely on destination nat for their security.

Firewalls are still usefull. it can be a device other than your host that can block of connections and do complex routing. such as l2l VPS and BGP routing. I personally would like to have them to help line private networks across my clouds in vpn tunnels