Can Exogenous Variables Be Used for Forecasting?

If you have scheduled events like a concert or this or that, then you can use exogenous variables in your time series forecast. But if not, exogenous variables aren't super helpful for forecasting inference and inferencing. For example, let's say we got our hot dog stand in Central Park and we're trying to forecast how many hot dogs and buns we're going to need over the next three months. We could try weather. You might be accurate for the next seven days because we would have a forecast probability of rain from a bunch of different weather services. And we could put that in so we could have one model that has that exogenous regresser of rain percentage per day