2 step
#2
It's like the factory rev limiter that you can set any rpm desired. Only it cuts spark instead of fuel. This will cause a turbo to spool up faster.
You don't need that with the blower BUT I like them because I use a trans brake. While on the break I set the 2 step at 3k rpms. I can sit there for long periods of time without hurting/heating up my transmission.