When I was able to see, in realtime, for example, I had a 500 calorie deficit today, and should hence lose 1lb in 1 week at this rate, and see it actually HAPPEN, it created a positive feedback loop. For the first time in my life, over many types of eating, some vague diet attempts, some periods working out more, some periods working out less, I could FINALLY see a direct result from my activities.

I had avoided it for a long time because I thought it would be miserable and tedious to track what I eat, but it's actually made it much easier to be disciplined, and see which foods are 'worth it' and which aren't.