Cyclist looking to eke out performance gains should track body weight using an accurate scale. This can yield insights into gains or losses, including fluid loss before and after workouts and races, when changing training altitude, illness, etc. Here is one example of a steep weight loss trend that indicates physiological changes.
The Alta Alpina 8-Pass Challenge was June 30, after which I developed a urinary tract infection which took a week to recover from (with antibiotics).
The graph snippet shown below shows a very interesting downtrend (red is calorie surplus/deficit, blue is weight). Weight was stable in the 10-day period following the event, but observe the steep downward weight trend starting June 10!
Once-per-week weight checks (ill advised) lack context, and hide this kind of intriguing pattern, providing zero insight into physiology, dehydration, etc. A scale with poor precision is also problematic, because the patterns will be polluted with measurement “noise” (accuracy is not important, but precision / repeatability is what matters, usually both come together with a quality scale).
I was not dehydrated these mornings when weighing in. Rather, it shows that once the trauma was over (the event and the infection), the body had some business of its own to attend to (perhaps shedding excess fluid needed for recovery)— weight (fat) loss is like that; just when you’re ready to give up, the body suddenly takes phsyiological action.
Longer term graph shown below, click for more reading.