The thing about outside, though, is that my garden is so tiny a clothes line or twirly thing would have to go right in the middle. It would really omit the play potential. A nice footy training pitch for my dc is worth far more that 15 pounds per year to me.
Environmentally, I'd have to balance it against the fact that lots more clothes would get spoilt in a small grubby garden with kids around.
the main thing is that my tumble dryer is upstairs, so I can unload it straight into wardrobes while I'm supervising bath time. My mum dries in the garden, and there is a permanent trail of half unloaded laundry baskets going through the house.