Cutting back big limbs on trees is generally discouraged during the growing season, but winter is an optimal time to prune trees.
The reason winter is a good time to prune trees is because now that the leaves are gone, it’s easier to see the shape of the tree and determine which limbs need to be trimmed back.
Plus, pruning a tree during the growing season presents its own set of problems, particularly because doing so can strip bark off of the trunk, exposing the tree to bug infestation and the elements, which can result in decay.