Transient controllers just make a sudden effect on every hard attack. If you pull the attack down it practically flattens the peak. Its very efficient and works in both directions without touching anything else. No pumping, no distortion.
I use it all the time to tame hard hitting peaks or to do the opposite if i need more peaks. Its also a quick way to lengthen or shorten kick and snare drums to fit the groove. In this case the sustain parameter does the job.
Greetings
Eli