 It's important because often what that creates is stem girdling roots. Next of all, you need to dig the hole two to three times wider than the root ball. And you want to make sure the sides of that hole that you dig are sloped and unexcavated and firm at the base. Remember, dig that hole to make sure the depth of the root flare is located at the very top first order of roots and the finished grade. We don't plant trees on a mound.