They're like money trains, only not.
Ghost money doesn't have to be burnt in big packages or by the sheet. If you really want to send a big offering, you can give one of these to be burnt. I have no idea how long it used to take. I seem to remember someone mentioning that they used to make all kinds of things (and still do?) out of ghost money/paper and then burn them as offerings - houses, cars, I guess any symbol of luxury. No confirmation on the veracity of this, though. Well, Wikipedia says it happens, but I guess it's in China, as I haven't ever seen that here.