Why do you need to be able to operate a camera manually? Because it gives you an idea of what values might fit a situation. The same way you need to know arithmetic even if we have calculators.
So here’s a rule all photographers need to know. A rule of thumb – that’s all it is of course – but a useful one. Namely, the “sunny sixteen rule” for exposures at mid-day:
Selecting these values will give you a “good standard exposure”. Of course you adjust when it is not mid-day, or you are a very high latitudes, and so on.
If you do not yet know it, learn this “rule” today. It’s great to be able to shoot without a light meter sometimes.