'Calories in, calories out' has been pretty widely debunked - at best it's part of the story. More important is meal timing (i.e. fasting), resting insulin levels, the source of those calories, etc.
Could you provide some sources? This is the first time I'm hearing of this.
On the flipside, you can increase calories out by exercising but you could end up starving and/or exhausted as your body tries to compensate for the increased activity, depending on what is going on in your body hormonally. Or you just have no energy to spare for exercise as it is right now, and have a very hard time getting in to an exercise routine. All this is to say that "calories in = calories out" is all fine, but these variables are not independent. Having some knowledge of how and when the human body burns fat and when it stores fat goes a long way in coming up with a strategy to lose weight. This is where these trends of low carb diets and (intermittent) fasting have originated from.