So for example of an unmodded controller, the Famas in COD:MW2 shoots 3-round bursts only. And there is a noiticeable delay between each 3-round burst that is fired.
With a controller with jitter mod you can actually reduce the delay between the 3-round bursts. Meaning you'll burn through a clip much faster. The jitter mod in regards to the Famas I find most useful in close combat when hipfiring, if I miss the guy on the first 3-round burst, I don't have to wait as long for the second burst to come out of the gun.
I'll be releasing a new high speed jitter mod for our COD:MW2 driver, it's just the jitter mod all over again, with the speed set even higher. This will result in the famas actually firing 'single' rounds continuously, instead of firing 3-round bursts.
Now this comes with some drawbacks. You'll notice any mod shop running the jitter mod that the gun tends to unscope, so it can be hard to aim with the jitter mod on. The jury is still out on whether the famas loses a lot of accuracy with the high speed jitter mod turned on, which is why I have only released the 'slower' jitter mod above.
Hope this makes sense, sometimes it's just easier to show it in a video.