Once you cut into old wood on leylandii they don't sprout back and look
very
ragged. We advised a neighbour of ours not to do this, she thought she
knew
better and she's now left with trunks sticking out of the top of lower
growing foliage looking simply awful.

Yes, down my street there's a 12' leylandii hedge on the boundary between 2
front gardens. On the owner's side they've maintained it well and it looks
quite handsome. The other side has been cut back almost to the trunk and is
a horrible wall of brown with not even a hint of green showing.