Even if you don't actually count calories, keeping a food diary is a good idea because it makes you more mindful of what you've eaten. It's so easy to just grab something from the fridge or the cupboard, eat it quickly then forget about it.
I watched some of that Michael Mosley show a couple of years ago about the Fast 800 diet and they advocate only eating when sat down, without telly, radio, books or anything really distracting you. So that you take the time to enjoy the food and remember eating it.
It makes sense to me because I'm always on the go (full time big job, kid with activities, house) so tend to grab a chocolate bar or a pepperami and eat it as I'm walking from the fridge to the living room so it's gone before I've even really noticed I've eaten it, then I forget and have something else.