scubagirl15:If you're assisting an instructor in training sessions, the IM helps you be a more effective DM, i.e. one who anticipates the instructor's (and students') needs, and to be that, you must know what it is the instructor is trying to achieve with the students.
Also, your knowing the standards and performance requirements means that if the instructor asks you to help a student one on one, you know what the student is supposed to accomplish.
I don't know what location you're based in (your profile doesn't say), but if your primary role is to lead guided underwater tours, I can see why you'd be puzzled by the need to have an IM.
If you read through your PADI DM manual, you'll see that it covers this topic quite extensively.
to pass exam questons you nedd one, ratios and standards etc.