Small, manageable, tangible goals are the key to weight loss, and tracking ones weight and intake meticulously allows you to set such goals.
For example, let's say I'm trying to gain 15 lbs this year. That's 0.28 lbs per week, or 1.25 lbs per month. My weight might go up and down a couple of pounds throughout the day, depending on the amount of water in my system, when I use the washroom, etc.
So, I weigh myself today, and let's say I had a little extra water in my system. Now, I weigh myself in a month, and I'm slightly dehydrated that day without realizing it. I might have reached my goal and gained 1.25 lbs that month, but the scale is showing I weigh 1 lbs less than when I started.
That's a problem, because I stuck to my goals, my routine, and I get slapped in the face with results that say I'm going in the opposite direction. I might incorrectly make changes to my calorie count, that don't need to be made.
This is why tracking is useful. You step on the scale on a regular basis, and you can see the overall trend over time. In the above scenario, I can see although the scale shows 1 lbs less, it's an off day, and looking at the forecast, I'm on target and did average a gain 1.25 lbs that month.
Now, I don't even have a scale, but that's why I'd like to get one, so I can step on it throughout the day, and see a graph to better summarize what's happening.
Wouldn't it just be easier to weigh yourself once a week, and if your weight goes up, eat less calories the following week and/or do more exercise? Unless your memory is that bad, or your eating patterns that random, it should not be hard to cut out things you know are high calorie and you can do without.