Not sure just what you are refering to, Mona, but this is not something that I would do.

Certainly not deliberately at any rate.

Nurseries remove most of the fine roots for bare root plants as they desiccate quickly and it is cheaper to post them. Fine roots also re-establish quickly and after a few years a bare root plant is more established than a pot grown variety as pot grown roots are used to growing in confined spaces and do not have the need to grow out as much.

The fine roots are also removed on bare root cactus, and some other succulents, to reduce the chances of rot developing after replanting. Other than that, or on the bare root deciduous plants Kildermorie mentions, removing the root hairs is NOT recommended--though at least some damage is inevitable, when transplanting.

if you mean the fine roots they are not root hairs. the removal of the fine roots stimulates the formation of new root growth. this new material will produce root hair cells. it is these root hair cells that are main source of water uptake. Water will enter and leave all root cells by osmosis. the most efficient part of the root for this is the root hair zone however.

When I split plants like primulas I always ruthlessly cut the leaves back to a few inches and also the roots to approx. one inch. I understood it was to encourage new roots.

I am not familiar enough with the perennial primulas to know, but I suspect that you will get better results by only pruning the roots that have gotten mangled in the digging and splitting process. That might also allow you to leave some of the youngest leaves at full length, resulting in a quicker recovery.

I definitely get better results doing what I do. The leaves need to be cut back anyway after flowering. They grow like topsy in our garden.

Ok, Scotsgran! There are a few general principles to gardening, but every species has its own preferences. : )

My book says, 'During transplantation the root hair are removed, that is why, the plant remains wilted in the new habitat.'

Ah! That means that the root hairs are accidentally (and almost inevitably) removed in the act of digging it up, or if the root ball falls apart in moving. It's not something that most gardeners would do deliberately. Ways to reduce the damage are to do the transplanting during cool, humid weather, if possible; get a root ball as large as you can comfortably handle, and keep it from breaking up when taking the plant to its new home. It is also a good idea to prune a plant somewhat immediately before transplanting--or immediately after--to reduce the strain on the remaining root hairs. It's a balancing act: The more leaves and stems that you can leave on the plant, the faster it can grow new roots and root hairs, but the faster it will dehydrate is the root damage is too severe.