You may probably ask yourself what is 'canopy management' and why would you need to manage the vines canopy. A simple answer is to expose the vine (i.e. the grape  bunches in the growing zone) to as much appropriate (direct and indirect) sunlight as possible and give each cluster, bunch of grapes the best possible chance of achieving full physiological ripeness, flavour and varietal character development.

A complex series of techniques including: vine spacing, trellising, shoot positioning, and leaf removal to improve both light and air circulation in an effort to create the optimal grape-growing environment for maximum flavour, colour, and ripeness of the grapes.

 

Such techniques are and should be very specific to each vineyard site, contingent on such things as soil fertility, grape variety, the age of the vine, unique microclimate and seasonal influences. Proper canopy management can affect the colour, flavour, and/or structure of grapes. It can also help prevent disease problems.
For instance, the careful removing of select leaves and shoots improves aeration, thereby reducing susceptibility to excess moisture inside the canopy - leading to rot and mildew on grape bunches. There is however a fine and careful art to removing excess foliage and it can be different with each new growing season.

Enough healthy leaves must be left on the vine to provide the required energy for grape maturation (i.e. maximum sunlight interception and optimum photosynthesis); excessive leaf removal can bleach the fruit's colour, cause sunburn on the surface of the grapes skin, or even impede ripening of the bunches.
On the other hand, vineyards growing in warmer/ drier areas require less leaf removal than those in cooler/ moist climates. In the end, good canopy management - with the result of the perfect balance between vine growth and grape production - meaning the difference between an ordinary wine and one of distinction.