Unfortunately, every bit of garden paved over is another bit of nature lost and another car on the road and at least one fewer person walking or cycling. That's the true cost. People also grow into their surroundings, which if they look like the car park of an abandoned retail park is some dystopian near-future, explains much of modern Britain.
I don't do any gardening, I pay a man (ok, usually three of them), though I did mow the front lawns of ours and next doors' yesterday, owing to the fact that the grass waited for the gardeners to leave after their last visit. I left the back garden though because of the perfect confluence of laziness and leaving a bit of nature around for the bees and assorted other bugs. Though at the moment I can see Little Monster Cat's ears in the middle of it all. She likes to think she's stealthy.
I mention the impressively useless extension our first house has acquired elsewhere. While the house was best described as compact and bijou (or in Estateagentese surprisingly spacious) it offered nothing other than putting the kitchen in the living room and reducing the garden to a cheerless square of paving for the Saddest Little Barbeque in SE London. Of course, ker-ching, it's now a three-bedroom house even if you'd struggle to get a single bed in the former kitchen. The kitchen was so small we risked inadvertently starting a family by turning around too quickly.
Reminds me, when we looking last we saw a place billed as 'four-bedroom' in Bromley. Seriously, two of those 'bedrooms' wouldn't have fitted single beds, the third maybe a single, and only the fourth was ample enough to earn to sobriquet bedroom. They'd basically taken a two-and-a-half bedroom house and upped the count to four. I remember that one because I cycled past some months later to see people trying to get a bed through the front door (the hallway was blessed with a turn sharp enough to guarantee impregnability to any furnishing that wasn't still flat-packed). Even the expedient and taking it around the back and through the kitchen, well, you still had to navigate that hallway to get it up the stairs. I suppose that solved the bedroom problem, not need to worry, you're not getting a bed up there in the first place. I have no idea why someone bought the place, the failings were obvious and it wasn't even especially cheap.