It is the one figure that cannot be gamed
A good month of low spending can be funded by a credit card. A pay rise can disappear into higher fixed costs. Net worth — everything you own minus everything you owe — catches both, because paying down a balance and saving cash move it the same way.
Expect it to fall sometimes
If you hold investments, net worth will drop in some months regardless of your behaviour, and that is not a signal to act. This is why the trend over a year or more is the thing to read, and a single month mostly is not.
It is also why it helps to see assets and liabilities separately. Net worth falling while your debt also falls is a market movement. Net worth falling while your debt rises is a different problem entirely.
Review it monthly, act on it quarterly
Monthly is often enough to notice a trend forming and rare enough not to become anxious about noise. Decisions — changing a contribution, switching a payoff target, revisiting a goal date — are better made against a quarter of data than a week of it.