Writing the most efficient programs possible.
Extremely powerful and extremely small, you can write an Assembly program in a few kilobytes that would consume dozens of megabytes in C or C++. It's barely above machine language, and generally you take much more direct access and control of hardware than is possible with pretty much every other language.
As per the thread title, if you are a real hacker, you know how to write efficient & compact Assembly. You might not use it all the time, but it's a skill that you polish. You can write bits of code that will slip in with other programs and never even be noticed, and it will transfer & install so fast and with such high priority that it's hard to detect or stop.
More than just the efficiency of Assembly itself, the sort of person who dedicates themself to understanding & composing in it also has very deep understanding of hardware devices and operating systems.
This, the surgical instruments. Assembly is akin to performing perfect neurosurgery while most other languages are like trying to use a sledgehammer as a screwdriver.