It would break with any updates, half the time xcode just wouldn't work, and it would sometimes be so slow that you'd need to wait minutes for some fancy animation to run.
And this wasn't even to get around buying a MacBook, we had one, I just wanted to compile and sign a hybrid app for iOS easier than using another physical machine.
Then we also found later that you can't sign an app on OSX while SSH'd into the machine... It just fails with a generic signing error.
So now I have a MacBook with remote-desktop software that's just permanently on in the corner of the room so I can open the GUI once a month or so and re compile and sign the latest version of our app...