As like many things, too much of any substance can be impacting your body in certain ways without us knowing.
There are however some benefits to drinking coffee or any form of caffeine before a workout. According to a study published in the journal of applied physiology, it has shown that 2 8oz cups of coffee can make a workout more enjoyable for individuals. Subjects have stated their workouts seemed easier with caffeine. Caffeine also enhances fat burning in people who exercise. This could be beneficial to the average person who wants to get into better physical shape. The study has proven that about 15% more calories were burned with caffeine before a workout. And lastly we all know that caffeine will increase our energy levels which increases our performance.
As I stated previously, anything we intake in abundance can be harmful to our bodies. The normal range of caffeine the body can handle is up to 400mg of caffeine in a day. That correlates to about 4 cups of coffee. Caffeine's job is to stimulate the adrenal glands which then release adrenaline into our body. This in some cases is a good thing, it puts our body into a state of “fight or flight”. This in turn raises the body's normal stress levels. Because of the stimulus to the adrenal glands, this produces that adrenaline at a “non-natural” time. This can burn out the adrenals from overuse which can cause a handful of issues. Some to point out are irregular circadian rhythms (your body's natural sleep schedule), fatigue, inability to recover post workout, and plateaus in your physical training (from the inability to recover).
All in all, it comes down to… are you someone that depends on caffeine to function or not. If you are, you probably have been feeling all of the side effects I mentioned and feel as though that is something normal. Bottom line is this, overconsumption of caffeine can and will limit your progress in the gym. As long as we are staying below the recommended healthy levels of caffeine, it has been proven to be beneficial to the body.