The API will respond with the requested data. If your requested location does not exactly match a grid point of the forecasting system, the API will automatically interpolate the requested location. The same will happen for any requested date which does not match a valid date of the model, where a temporally interpolated value between the two closest available valid dates will be returned.
When using latitude and longitude in the API request, their representation in the API response will contain at most 6 digits after the decimal point. This allows for a sub-m precision, but exceeds the resolution of most of the available data sets by magnitudes.
Please note that the returned weather data is likely to have changed if the same request is queried again later, such as when a newer run of the forecasting system becomes available.