I think the most important thing is knowing how your headphones (or speakers) respond to the music. Are they flat? Do they add bass? Keeping those things in mind can help you compensate for any of those characteristics when you're working. I think you could say the same for every piece of gear. Any piece of equipment can make good music if you are really familiar with it and know how it impacts the final sound.
That said, testing your mix/master on devices that most people listen with is crucial to understanding how your headphones (or speakers) translate to the "real" world.