For starters its hands free, so useful if you have to walk another dog or do things like go to the bank etc. The pouch I got sits at the front and fastens like a back pack around your back and waist (there are two sizes: small, up to 10 lb nd medium, 10–20 lb). I felt silly at first but everyone I met thought it was such a good idea and either wanted to know where I got it from or wished they'd had one when they got their pups.
I got mine (made by Kyven: Outward Hound Pet-a-Roo) from PetPlanet (
http://www.petplanet.co.uk), but I think PetPack (
http://www.petpack.co.uk) do them as well.
Even though Wilf now walks well on the lead I obviously can't exercise him for too long so the carrier is going to be invaluable at the weekend when I take my other cocker on a long walk. I had to get a harness for him so I could clip him into the pouch as he could slip out. In between me using it for long walks a friend is borrowing for the cav pup she gets tomorrow.
And when you think you might not get any more pups you could always pass it on to a rescue or charity who foster pups out before going to a new permanent home or training for, e.g. dogs for the deaf, etc. I'm keeping mine as I want to hopefully foster pups in the future for rescues or dogs for the deaf.