We all make mistakes while typing, especially when we type very fast. While auto correction in Mac OS X Yosemite and Mac OS X El Capitan is a handy tool, it is not completely reliable. Being a spelling auto corrector tool, it sometimes changes your words or guess wrong words as corrections. This can end up in more editorial work than if auto-correct weren't running.
When you are drafting a letter in English, auto-correct comes in really handy. But the auto-correct will often lack context and will replace mis-spelled words with words that don't fit the context. That's a problem because you can easily miss the correction unless you proofread thoroughly. That is why some folks turn this feature off.
How to Turn-Off Auto Correct in Mac OS X Yosemite and El Capitan
Step 1: Click on Apple Menu.
Step 2: Choose System Preferences.
Step 3: Click on Keyboard.
Step 4: Now, click on the Text tab.
Step 5: You will see a checkbox in front of the option, Correct Spelling Automatically. Uncheck this option and you've turned off auto-correction.
Any app that uses the system auto-correct feature will no longer auto-correct mis-spelled words. In apps like Pages, Notes, TextEdit etc. where the mis-spelling is underlined, you'll be able to proofread easily. In other apps, you'll have to wear the editor's spectacles.
The feature can be turned on back again when you feel like getting auto-correct's assistance.
We haven't heard much about how good the auto-correct's contextual-abilities have gotten in Yosemite (OS X 10.10) but I think Apple would have punched in some cool features for this. In iOS, we still end up with funny autocorrects (an entire cult has already been established). OS X's auto-correct disasters aren't all that popular (largely because you aren't typing many informal messages in Pages or TextEdit). Nevertheless, should you find the auto-correct annoyingly obtrusive, you now know how to turn it off.