Simple, when performing various git annex command over ssh, in particular a multi-file get, and using password authentication, git annex will prompt more than once for a user password. This makes batch updates very inconvenient.
I'd suggest using ssh-agent, or a passwordless ssh key. Possibly in combination with git-annex-shell if you want to lock down a particular ssh key to only being able to use git-annex and git-daemon.
Combining multiple operations into a single ssh is on the todo list, but very far down it. --Joey
Unless you are forced to use a password, you should really be using a ssh key.