Sorry, I am being dim, rather stupidly I thought you were questioning whether to plait the mane! So my answer referred to the mane. (Sorry I appear to have lost the ability to read!)
WRT tail it does not matter, in dressage they tend to like the unpulled tail I think.
You've peaked my interest I'm not too up on the horsey thing & I have a dressage comp next week. In the passed I've generally done ok but what sort of things keepa judge on your side? I was thinking of taking them a cup of tea with some home baking before I started?