I see we can add ssh keys in DigitalOcean Dashboard (https://www.digitalocean.com/ssh_keys).
I would like to the know use of it against creating a user in shell and adding ssh keys at .ssh folder of the user.
When you create a droplet, it will add that key for you for the root user. You have to select the key during the create process. Afterwords you can move the .ssh folder to whatever user you create that isn't root (assuming you do that).