stealth camping is an interesting concept, with quite a few interesting applications. Like the ones mentioned above, camping in closed parks, getting closer to wild animals (not many of them in Britian, just foxes, badgers, owls etc) plus its supposed to leave no impact to the enviroment around you
Last year, I swapped over from tent to hammock (I got myself a hennesy) simply because I was tired of waking up in the morning either swimming in water or with a pretty bad back ache, them spending 20mins trying to get the blasted thing squished down enough. Dont even have to worry about finding a flat bit of ground, just two trees.... or maybe a telegraph pole, drain pipe, sign post, luggage rack, etc
I can put my hammock up in 2 mins, and it comes down in 46 seconds (seriously, we timed it) which is very useful, for not only starting my day earlyer, but it also means I can keep going for longer, and cover more ground. I am also not worried about getting myself to a camp site. I havent done it myself, but I do know of people who have actually slept on the footpath (well, right nxt to it anyway) because it got dark. Its not exactly legal in the UK, but quite the definition of stealth camping I believe.
I also help out with Duke of Edingborough award (its an after school activity aimed at under privilaged kids, getting them to do new things like camping, comunity service, first aid, sports) and when your looking after 30 or so teenagers, you need all the time you can get to keep an eye on them (plus, they take all the good camping spots)