When setting up Messages (whether on iOS or OS X) we’re asked how to start new conversations. The options offered in Settings are typically an iPhone number or two email addresses. I’ve always opted for the phone number. Does it matter? Presumably the option chosen (e.g. start new messages from an iCloud or Gmail email address) must be the same on my Mac and iPhone. But will it make any difference to how well the app works and how quickly messages I send sync between all my iOS and OS X devices?