Dormant pruning happens during winter, while the plants that benefit from it are dormant. Obviously, it would not be dormant pruning otherwise. Such processes are less stressful to plants while they are inactive and essentially anesthetized like a surgery patient. This is also why fresh bare root stock becomes available and ready for planting during winter.
Bare root stock grows on farms for a few years. Any grafting is part of the process. When stock is sufficiently mature, growers dig and separate its roots from the soil that it grew in. Much of the stock goes to retail nurseries for heeling into damp sand for sale. Some gets neat packaging with damp sawdust around its roots. Some goes out for mail order sales.
Regardless of the process, it all happens quickly and early during winter dormancy. Bare root stock must then get into soil again, quickly and before the end of winter dormancy. It will not survive if it resumes growth without soil to contain new roots. Planting should be as soon as possible, so that roots can settle in with rain, and be ready to grow by spring.
Bare root stock is less expensive than canned (potted) stock because it is so lightweight and easier to process. Since it occupies less space than canned stock in retail nurseries, more varieties of bare root stock are available. Bare root stock is easier to load into a car, and plant into a garden. Once in a garden, it disperses roots quickly and more efficiently.
Deciduous fruit trees are the most popular bare root stock. Of these, most are stone fruits or pome fruits. The stone fruits, of the genus Prunus, include cherry, plum, prune, apricot, peach, nectarine, their hybrids, and almond. Apple, pear, and quince are pome (pomme) fruits. Pomegranate, persimmon, fig, mulberry and walnut are somewhat popular as well.
So much more than deciduous fruit and nut trees are available as bare root stock. Grape, kiwi, currant, gooseberry and blueberry are deciduous fruiting vines or shrubs, not trees. Blackberry, raspberry and strawberry are evergreens. Rhubarb, asparagus and artichoke are perennial vegetables. Rose, wisteria, hydrangea and so many more are fruitless ornamental plants.
Tony Tomeo 
I remember getting little bare root trees for the nursery when I was a child (and planting them as well). It always seems miraculous that you can dig something out, clean its roots and then stick it back in the ground before it starts growing again. Do the roots get trimmed when this is done? Or are they usually limited enough?
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Roots get pruned in the process of digging. Roots that might get broken in transport can be pruned at planting. I do not bother, since new roots develop from the break as easily as they develop from a pruning wound. Root pruning should not be necessary for trees purchased from nurseries. Trees that get dug from the home garden for relocation will need root pruning though, just to get them out of the ground.
Although root pruning should not be necessary, the branches of bare root trees will likely need pruning. Such trees come with extra growth, partly as packing material for transport, and partly to provide more options for pruning when the trees go into the garden. For example, upper growth can be pruned down to promote a lower branch structure. Alternatively, lower stems can be pruned away to promote a higher branch structure. Stems that get damaged in transport should be pruned away first. Some small trees may not need pruning, and some may not be branched yet. Also, cane berries just get plugged without pruning. A new cane emerges from the roots, and the original stubbed cane can get pruned away later or next winter.
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Thanks!
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You are welcome.
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