Environmentally, I absolutely agree, hedging is a real boon in helping air quality, thats a really good point. I'd definitely investigate rate of growth of the plants though. Laurel is as bad as leylandii at growing fast - I have laurel hedging at the bottom of my little suburban garden

Last year, after I'd been ill for a while, we took two Luton vans worth of hedging to the recycling centre

and this year, there was another twelve feet of growth to cut down. A couple of the trunks are too thick to saw through with a hand saw, and a neighbour has offered to bring his petrol powered chainsaw over. I've now got two layers of laurel trunks about 8 feet high, and one that I've lopped at waist height. It has to go to the recycling centre - the greenery has quite a high proportion of cyanide, you can't burn it!
The greenery is still growing at a rate of knots, but the soil is still fertile - sweet peas have colonised since I cut the laurel last year, they've taken over the first four feet. Between that, the rhodendron shaped like a tree, and my quince, the garden is actually noisy with the sound of bees
