Crank sensor issues

[DoreSlamR]

Evening all

I was wondering what exactly the crank sensor is for? its located above the crank (duh) at the front of the motor.

I'm asking because initially i thought it was the cause of a small oil leak i have got, but i'm unsure.

Its hard to tell because where ever the oil is coming out its right near the belts so it ends up being sprayed.
so if its not the sensor what might it be? any suggestions would be appreciated!

Chad