The way we write is on many occasions a faithful reflection of how we express ourselves and for informal communication or even for save time in some other writing we can resort more than once to keyboard shortcuts that will convert our abbreviations into complete words.
For this, both OS X and iOS both have a spell checker that includes an autocomplete of expressions that is reflected in the system as «Quick functions», this will make that when we write for example 'xq' it modifies it to 'why' to save time, among other abbreviations that we personalize.
To start in both systems we must have iCloud feature enabled with our Apple ID and have the box to synchronize 'Documents and data' checked in both so that when we modify the abbreviations they will appear in real time.
Once we have it activated, it will only be necessary to add those keyboard shortcuts both in one system and in the other, regardless of which one, since as I say, it will be completely synchronized. In OS X it will be enough to access the menu > System Preferences> Keyboard> Text and add the abbreviation while in iOS we must go to Settings> General> Keyboard> Quick Functions and add our abbreviations.
In addition to this in iOS we have the possibility of use shortcuts in phrases with abbreviations so if we use a specific phrase a lot we can summarize it in just a few letters.
In general it is an option that, in itself, seems quite useful when we have to carry out very extensive writings It is appreciated that the possibility of having these quick functions synchronized on our Mac and on our iOS devices is also included.
More information - See how your Mac works on Mavericks with Systemstats