"It's really easy to turn off with some simple code or one of a bunch of plugins. The AutoP shouldn't mess up your code at all if you are building it in the text box and not the visual editor, unless you are doing something pretty wonky. As for why it exists, as far as I can tell it is mostly there to keep users from making terrible looking websites by having a lot of badly crunched together text. IMO that's a good reason. Why does it modify the output of text entered into the Text editor? Because it modifies output, not input, which means that this occurs on the front end. If you are writing sane HTML, it should have little to no effect. On a more technical level, WordPress doesn't distinguish input from the Visual vs Text editor as far as I know, so it would be difficult to filter the display of the results based on that. Having a checkmark to turn it on or off is likely the best way to go." - Aram Zucker-Scharff