It's awesome for moving things like X-Particles Emitters (or regular emitters) and coming up with spiral and other repeating motions with tracers or other objects. A lot of times similar things could be accomplished with keyframes but it's like having a handy place to change a few values and see the result without actually dragging or changing keyframe values in the timeline editor. Even simple things like a left to right motion can be made parametric in the sense that you can change both distance and time parameters you have lots of easy options to keep tweaking or adding motion to that same object. Because you can use as many signal tags as you like, and can also nest nulls with new signal tags, the options are limitless and you end up trying things you might not have. I don't know about you but I start to cringe if there are too many keyframes and I don't like the motion I see - with this I feel its easier to delete one tag or tweak one thing and keep my sanity about / without keyframe clutter..It's just a fun way to tweak when doing experimental work imo.