so is this harmful or are there any side effects to this? similar in the aspect that a FCD can harm your engine, do these cause any adverse effects?

 

You can only raise the amount of boost with a boost controller, not lower it below stock etc("stock" boost level changes though once the wastegate is ported of course).

 

ooohh well see...you learn something new everyday!

 

You can't lower your boost beyond the point where the wastegate hole is too small for all the exhaust gasses to escape (creep).

 

the ball/spring controller works by blocking flow to the WG until a certain boost is reached. Basically, you tighten the spring to 10 psi lets say. The boost controller will remain closed (so the WG sees no pressure) until 10 psi is reached, then the ball will be pushed back and air will flow into the hose attached to the WG, opening it.

An FCD will only lean out the mixture if the fuel system cannot supply enough fuel. The ECU will use the signal from the AFM to determine how much fuel to supply, but if either the AFM gets maxed out (not sure how much it takes to do that, but it would take a lot), or the fuel pump or fuel injectors get maxed, then you will run lean. All the boost sensor does is move the boost guage, and initiate fuel cut.