I've been working out for over year. I've got to the point in cutting where I'm not putting any more muscle on (calorie deficit), I'm also measuring so I know if I'm losing muscle or not. Therefore, a drop in weight (<2lbs) is mainly fat loss as far as I'm concerned BUT that is ONLY because I know my own body. Each is his own, but when you've been working out for a while and keep track of things, you know what's what
I'm very goal-driven so simply looking in the mirror isn't enough for me, and without keeping track of things you could be wasting your time without even knowing. I guess it comes down to how committed you are. That's my view anyway.