Posted: 31/07/2016 at 11:42
depends what you want GK. There is no 'have to' about pruning, those that have gone feral don't get pruned.
Pruning stops them getting too huge, a lot of gardeners don't want too huge.
and some naturally develop into better shaped trees than others.
Once they've had the cut back treatment they never make a tree shape though they may do a very large bush.