Now is the worst time of year to prune and trim trees (not including branches that are obviously dead or diseased - trim away on those). Trees with live branches will suffer if trimmed now, and pruning in the fall is even worse because it prevents the trees from going into dormancy.
Healthy limbs should only be removed in the middle of winter — the dormant period when the tree is asleep — or in the spring when the tree has just begun actively growing again and new growth is forming naturally.
Pruning during the growing season always stimulates new growth. During summer’s heat, having to produce that new flush of growth greatly stresses a tree. Wait for winter - the best time to trim!