You don't have to use this all the time. The only time it would be required to use this is if you have two variables with the same name - one a local variable, and the other a member of a class - and you want to differentiate between the two, then you would use this. Same with super.
Yes, it is true that you can do that with Processing within java, however for large programs where you are more worried about separation of concerns, then you'll want to structure things differently and will probably have to make explicit references to a PApplet class.