How will the recent appearance of a supernova, the closest in 27 years, help reduce the uncertainties in our measurements of dark energy?
The current supernova is a supernova of type Ia. Supernovae of type Ia are used as standard candles for distance estimates, especially used to determine the Hubble constant. Hence by a better calibration of this kind of supernovae, more about the reliability and accuracy of distance estimates can be learned.

The expansion rate (in relation to the distance) of the universe, expressed by the Hubble constant, is an important incredient for the estimation of the fate of the universe.