What are advantages and disadvantages of insulin treatment?

On the positive side for insulin, it is always effective provided the proper dose is used. This is true for people who have elevated blood sugar levels first thing in the morning. Many other diabetes medications are not very effective in this situation. The dose of insulin can be adjusted in very fine gradations, which may allow for more precise control of the blood sugar. Insulin varies quite a bit in cost depending upon what kind is prescribed and how much is used, but it is less expensive than many newer diabetes medications and at least some forms of insulin are included on nearly every health insurance formulary (list of preferred drugs) because the insurance company knows that insulin is essential for such a large number of people.  

On the negative side, insulin carries a high risk of low blood sugar reactions if too much is used, and many people gain weight when treated with insulin.  

Notice that I did not include the fact that insulin is given by injection as a disadvantage because in my very strong opinion -- an opinion shared by almost everyone who treats people with diabetes -- the injections are quick, easy and cause very little discomfort. I have almost never had a patient who didn’t say, “what was I worried about?” after just one or two shots of insulin.