I very recently inherited an Umbrella Cockatoo from a friend who became to ill to care for her. When we were going over all her care instructions she told me that she brought her to a local bird specialty store regularly for grooming and usually the charge for this grooming is $40 and since I was helping her out she wanted to pay all the birds future grooming appointments for me. I asked what exactly was involved in the grooming and she said that they would pluck out several feathers from random places, long ones from her tail, short ones from her back, etc. The bird store lady's explanation of why this was necessary was very long but part of it was something to do with certain "bad" feathers were interfering with growth and causing the bird constant discomfort which will lead to insanity.
Now I have no intention of bringing this bird back to this place and allowing her feathers to be yanked out again. I have a decent amount of experience working with birds both as a technician for several years in an exotic pet clinic and with my own birds, and I have never once heard of this. I am wondering if anyone else has ever been told they need regularly pluck feathers from their bird or if this is just something that this bird store made up.