The most constructive use of your activity to monitor is to track NEAT (non exercise activity thermogensis). This means the activity you do outside of structured exercise.
The significance of NEAT is vastly under played. NEAT can influence your weight loss in two primary ways:
Reduced activity due to reduced energy intake
Reduced activity due to increased exercise
Both probably have subconscious and psychological explanations depending on the individual. For example, reduced NEAT after exercise could be explained by feelings of fatigue/soreness/lack of energy or by the idea that because you’ve exercised you can move less the rest of the day.
Your activity levels outside of structured exercise are likely going to be more important than your brief exercise session. There is a tendency to reduce your habitual activity levels when you’ve exercised. A good example is step count. You might force yourself to walk to the shops instead of driving if you’ve not yet met your step count. However, if you’ve exercised and have thus already met your step count goal you wouldn’t. In this instance you have (to some extent) compensated for your exercise by reducing your activity.
Your compensatory response in activity to diet and exercise is one factor that is predictive of your weight loss success. You could find yourself adhering to diet and exercise advice but not losing weight due to reduced activity levels. This can be extremely disheartening and is often met by accusations that you’re not sticking to the plan which is even more frustrating and demoralising. Monitoring activity levels may explain this.
It is also likely you’ll move more purely because you know you are being monitored.