I have never heard of such a thing here in Brazil, I guess it hasn't occured to anyone yet. It's something really stupid because if you are releasing them, you probably had to imprison them in the past. It is also sad because they die. I wouldn't like to start up my marriage on such a note. I had no idea people could do this kind of thing.
Butterflies represent freedom.
The really great feeling of being visited by a butterfly cannot be bought. They choose to come. You can't force them.