There are at least two versions of the C4 (are you talking about Studio Projects?) that I know of.
They have different switch configurations.
Which model do you have?
1 switch
or
2 switches?
Either way, there will be a '-Xdb pad' and a 'bass roll-off" (High Pass Filter).
The pad would just be for situations where the source is incredibly loud.
In a case like this you would have trouble setting your levels because you're stuck down in the first 2 or 3 positions. Setting the pad gives you more range to set your recording level.
The bass roll off (hpf) would be used to take some bass off your input.
I, personally haven't had much luck using this feature.
I've tried using it for bass heavy music to lighten the load on my recorder, but to little effect.
Hopefully someone else can give more detailed advice.
I'd be interested in hearing it as well.
btw There is also a Team Studio Projects with several people who have used the mics extensively.