Taking Sides

Those fast growing fir trees, Leylandii are as much a curse as they are a blessing, and it all depends on your perspective.
Yes, of course they provide an effective natural screening as a hedge, will add to your privacy, can hide an unsightly area of the garden and provide a natural wind break and sound barrier.
But their principal virtue in that they are the fastest growing confer we know, may also be their downfall.  They can grow up to three feet a year and providing the sound advice of keeping them trimmed at least once a year, they should not get out of hand or become a nuisance.
The key factor might well be how close a hedge is to a neighbour’s property and whether it is such a height to obstruct light from the nearest window.  There is legislation on high hedges under the Anti-Social Behaviour Act and local councils can take action if complaints are made.
Even a hedge which has grown to twice the height of an adjoining greenhouse so that it cannot be used for its intended purpose might well be construed as impairing the reasonable enjoyment of a neighbour’s garden, and fall foul of legislation.
We actually moved from one house when a neighbour planted a Leylandii hedge which obstructed our view of the open countryside. 
As I said, it all depends on your perspective — and which side of the fence you live.