Calories do matter. But not from an "I need to burn so many calories in order to lose weight" perspective. Really calories are just a total of what you consume at the end of the day and should merely be used as a guide to help you stay in line with what you are trying to accomplish. Although I do monitor my diet rather closely, I have gotten away from such strict adherence to calories and macro counting as it never really was a reliable source for me to lean on. I tend to focus more on how my digestive system feels, how my mood is, and my physical energy. Those tend to be the aspects for me that get disturbed if I'm eating too much or too little. But someone who has a specific goal may need to dial it in a little bit more. My personal goal is to have a healthy gut which impacts pretty much every aspect of your body....including your weight.
Too many calories can leave you with excess weight that you don't need to be carrying around. And too little calories can leave you in a deficit with not only weight loss, but body systems borrowing from Peter to pay Paul. This is where we need to pay attention. When the body starts to become depleted, the digestive system slows down and hormones go haywire, skin gets dry, hair starts to fall out, thyroid downregulates, and our energy is low and cranky. The first thing we would look at is what someone is eating, how much in volume, calories, and macronutrients......that being the carb vs fat ratio which are our sources of energy storage. Its a teeter totter of balancing everything and bringing it into line with what works for you always remembering that you will need to make adjustments depending on how you feel. If that is by adjusting your overall calories or by slashing your starches and increasing your fat consumption, you go by what your body is telling you.
There are too many studies to prove one theory and disprove another theory. At the end of the day, yes, calories do matter. But then again, it all matters. You will never know exactly how many calories or macros to consume. It's simply not possible to know these abstract numbers. But you can always know how you feel. I am not, and never will be, an advocate of any one specific way to diet, eat, or monitor your habits. I am only interested in how I/You FEEL!!! And that is probably the biggest aspect that is missing in this jigsaw puzzle of diet and lifestyle. Find the missing piece and you will put it all together.