Because there was a power cut and your development machine isn't online, or the cleaner pulled the plug on it or maybe the sysadmins decided to change the network settings over the holidays.
I was replying to the previous comment, trying to say that you can't always guarantee that a remote machine will be available. There are more benefits than just having your development environment always available though, like not needing to install or set up anything when moving between machines, or being able to extend your development environment using the same language that you are developing in.
