SPEED CONTROL VALVE  There are two types of Speed Control Valves.  One for how fast vehicle rises, and one for how fast it drops. Without regulating the speed of up/down, you will damage your suspension components and in time blow the seals in your Airstruts.  Speed Control Valves “Control the Violence”
Speed Control Up  If you have 8 separate valves it will take 4 Speed Controller Valves for up and 4 for down, for a total of 8.  (this is a big reason to have a Plug and Play or an Air-Engine, because it takes only 1 Speed Controller for up, and one speed controller for down)  
Speed Control Down installs at the exhaust port of each valve.  Again, if you have loose brass valves, it will require 4 of them.  If you have the Air-Engine, only 1 required.

It is true that if you do not have controllers, the vehicle will pop up/down even faster, but with speed controllers, it will still move fast, and you have the ability to adjust each one by your fingers