For centuries, fruit trees have been bred to produce unnaturally abundant and unnaturally big fruit. That has worked out well for those who enjoy the resulting fruit. It is not such an advantage for the exploited trees that must produce it. Without specialized pruning, most of such trees are unable to sustain healthy development of all the fruit they could potentially produce, or support the weight.
Specialized pruning concentrates resources into less excessive fruit of superior quality. It improves structural integrity of limbs that support the weight of all the fruit too. Trees that produce smaller and lighter fruit, such as cherries, may only need to be trimmed occasionally to eliminate structurally deficient growth. Heavier fruit, such as peaches, necessitates much more aggressive pruning.
Almost all deciduous fruit trees should be pruned about now, before they bloom and foliate at the end of winter. Such pruning is too severe to be done while the trees are active in spring. Summer pruning to maximize production within less space is the only practical option to dormant pruning. Evergreen fruit trees, such as citrus and avocado, should not be pruned or groomed during winter.
The main group of deciduous fruit trees that require dormant pruning in winter are stone fruit, of the genus Prunus. This includes peach, nectarine, apricot, plum, prune, cherry, various hybrids and almond. The second main group are pomme fruit, such as apple, pear and quince. Fig, persimmon and grapevines, as well as roses, need specialized and perhaps very aggressive pruning too.
Dormant pruning of deciduous fruit trees, roses and grapevines is too complex to describe adequately here in just a few paragraphs. Nonetheless, those who grow such plants must be aware of how important it is, and ideally, know how to do it. Nowadays, it is nearly impossible to procure services of horticultural professionals who know or care how to execute such procedures properly.