Depends what you want to do - it can be an advantage for jumping as horses with this find it easier to bring their hind legs underneath them. It can also be a sign of damage in the area as well I believe.
Can be a sign of wastage in sacrilliac(sp) so I would advise a little rest and build up of topline. I used Baileys no 4 for at and then do lots of hill work to build up lost muscle!
Its not normally anything to worry about at all. It can just mean they are maybe prone to sacroliac injuries, but tbh Ive known several with it that have never had a problem.