Think of exercises in the same way as your diet, more variety the better. I once learnt in a lecture that an average person eats no more than 12 different kinds of food in a typical week. Do you do the same with your exercise selection by doing the same exercises week in and week out? Have you been doing the same hand full of exercises for the past 12 months without any change or rotation system?
If so, then it is time to shock your body. Train to achieve a response from each workout with at least using the method of rotating your exercises frequently. Keep in mind there are many alternatives to the standard movements you are probably already using. Although you are basically doing the same movement you can change the response by using different tools and training principles.
You have less chance of suffering from ‘overuse injuries’ if you regularly rotate your exercises. Also the more you change your workouts the less chance your body will adapt to what you are doing resulting in a tougher workout with better results.