As you probably know, NovoLog 70/30 is a mixture of analog basal and bolus insulins in a fixed ratio of 70:30%. It's purpose is to reduce the number of daily injections you require by combining them. There are other mix ratios but 70/30 is by far the most common.
As with any insulin, it can cause a hypoglycemic reaction. You should take measures to avoid these and to treat them effectively. Your Doctor is responsible for educating you. Other than that, there are very few side-effects from insulin with the exception of a tendency to put on weight. You have to counter this with a light-diet and an adequate amount of exercise.
Don't regard using insulin as a sign of defeat. It you get better health as a result, you're wining.