Well, but lets say I have a cap of 15 happiness at the moment. If I stop growth, I'm capped at 15 worked squares. If I now rearrange my worked tiles so that I grow by two more every turn and my city gets to size 16, I'm still working 15 tiles and getting the most out of it. Right?
I can see the more maintenance I guess, but other than that, don't see how its a problem.
Edit: To clarify this more (because I understand what is meant about inefficiency), I make the assumption that I can't switch to another tile that will stop growth and give me any more production/commerce instead.
Well those conditions will never occur for unhappiness. If your happiness is capped at 15 and you produce another person, that population point will just be unhappy and do nothing but you still have to feed thier sorry asses.
So unless you're really close to getting a new way to make your people happy, I see no reason to ever let your cities grow beyond thier happiness limit.
As for health, if you find growing actually causes you more of whatever you're looking for...then go for it.
there are plenty of times to let your cities be unhealthy... that is not as much of a drain and sometimes the slower growth is desired. but I would never recommend having unhappy citizens, as they said they just sit there doing nothing but the key is you have to feed them (2 food per turn)... those two food per turn could be feeding a specialist or a worker who is producing gold and/or hammers. lot of people say food is the most important resource in this game and this is part of the reason why.
on the other hand, the changes they made from Civ III are a huge improvement-- now if you have unhappy citizens at least the city won't completely shut down. not to say you won't ever find yourself in a situation with unhappy people... sometimes it's a necessary evil, like if you are at war and can't control war weariness levels yet or something like that. but you should always keep an eye on unhappiness and try your best never to exceed the limits.