Do you really need an outline? Is that even a question that can be generically answered to fit every writer out there? No, not really. But what I can do is explain the process that has worked for me.
So if the question is: do I need an outline? And for me, that answer is yes, but the outline has to be done in a pretty specific way. The formula for it has been tweaked and redefined through project after project until something has been refined enough to work each time.