I track my food using one of the many great online apps (I like LoseIt, but there are other good apps as well). I track mostly to make sure my macros are in a good range for me, and to see how my weight fluctuates over the years. But it's also interesting to see the calories. (If in the afternoon I find that I'm way over my average calories, I probably change behavior for the rest of the day and have a lighter final meal.) The history on the app lets me know that macros matter a lot more than calories for my weight--the higher the proportion of fat and the low the carbs, for me, the easier it is to lose weight and then maintain. Your mileage may vary, of course.