I get it now. I asked my old trainer how to trim tails. She said 'you can pull tails, but it's a huge hassle and takes days.'
I can plait tails but I find it such a faff, it is an unneeded hassle on the day of the show when I have far more important thing to be doing with my time!
Plaiting tails also doesnt give the same shape and doesnt make the horses bum look as good.