Why would you think? Did you look this up in your pharmacology or med/surg textbook?
See, we don't do homework here. If you have confusion about something, tell us what you know and what you already looked up, and tell us why you are confused. Don't come asking such a basic question without even giving evidence that you tried first.
Think about what a sliding scale is. Does it make sense to give the same amount of insulin when your patient's blood sugar is 600 mg/dL as you would if your patient's blood sugar was 200 mg/dL? If not, then wouldn't a sliding scale make sense? Most diabetics have a "goal" blood sugar range and they adjust their insulin doses to meet that goal.
Good for you!!!! There are going to be many times something isn't going to make sense to you...a disease process that you have never heard of that you need to know about to care for your patient to the best of your ability....these are the skills that take a good nurse to being a great one.