Find out early what organisms and chemicals are in your fermenting juice.
Fermentation is the process by which the 'must' (the primary, soon-to-be-wine mixture) turns into wine.
Fermenting juice may not have sufficient quantities of complex character producing chemicals. Find out early.
If your fermenting juice has spoilage organisms at the start you can be sure your wine is going to express the character of those organisms. Find out before your fermentation starts and tackle any problems early.