Craig's advice recently encouraged me to plant deeper than I usually do and I do see the smart thinking of that advice as well. The basics I reckon is that if the root is deep enough it can have many side shoots so just like a branch that has all it wants it grows much quicker.
As most things like this I think it is variable with the material you are working with.
I planted out a couple of tridents on their second round of root work and this time I had to remove some high roots. Planting too deep after this would encourage this area to reshoot. So maybe I should not have gone too deep with these ones at least.
Although I recently shifted an older hawthorn that has a surprisingly great mature spread from little work. It was reduced hard with no top growth removed and I think planting it deep was advantageous because there is no fear of roots developing above the mature but largely reduced root base.
So many ways

No photo's yet I have at least one picture of a Trident I planted out the other day. Will post soon.