Having specific keys for specific purposes is more secure because when you add the public half of it to your SVN server, you put the extra options along with the key that limit the server it can come from, and the command it can execute. This means that your seemingly-scary private key can now do one thing and one thing only - pull from svn. Now you can do deployments without any constraints like "abhaga needs to be awake and have his computer on and be SSHed to the right places" :)