Why do you prune? To shape them, for sure. But also to give the plant/shrub more strength.
One of the key principles in organic gardening is to strengthen plants and eco-systems. Tune into the needs of your plants, shrubs and trees. It takes a little individual care along some basics. Strengthen them! Correctly timed pruning plays a big part and avoids chemical treatment!
Do you see how limp the new growth looks on these super healthy boxwoods? Trim them, so that the boxwood stops pushing all its nutrients to these new, weaker parts. Over time, it will grow denser / fuller and stronger as a result of your correctly timed trimming.
What shrubs should not be trimmed now? European hornbeams come to mind right away. Trim them when they are fully dormant. It is the last job in my garden just after Thanksgiving.
Trim rhododendron, azaleas, boxwoods, weigelia and boxwood in June so they can grow new flower buds over the coming summer months and get ready for beautiful flowers next year!