You don't need it, but it's recommended that you do if you want precision accuracy. Why?
No, not because longer/tighter barrels are more accurate. It's physics and aerodynamics. Given the fact that we play this game with very small, lightweight objects, it doesn't take much to throw them spinning out of balance. A small change of wind or pressure can throw off a shot at longer distances, so your groupings may not be optimal.
I could draw it out, but what happens to a bb when it leaves a 6.03mm barrel and enters a 7mm+ barrel (suppressor) with air still pushing behind it? Unless that bb is directly in the center of the air cushion, slight differences in air pressure can cause its path to change enough to throw off a shot. Couple that with the fact that you could be using a cylinder that was built for a 363mm barrel and it may not have enough air volume to push it through an additional #mm of barrel effectively.
Of course, this is the DMR in me speaking. There are many factors that would require a separate thread. But in summary, if you are worried about extreme accuracy, I would recommend lengthening your barrel when you put on a suppressor. Otherwise, throw it on and enjoy the eye-candy.
