My main 2 reasons for installing it both come from needing to restart services sometimes:
Portainer let me allow other people access to restarting specific containers that occasionally misbehave
Portainer lets me update and restart all of the containers running in my VPN stack without breaking. For some ungodly reason, even with dependency set and everything in docker-compose, a CLI reboot will basically always start a service or 2 before gluetun is actually advertising it's in a healthy state and everything breaks. With portainer that doesn't happen, with the exact same compose, and I don't get why lol