what's in a name

[Friedrich F. Grohmann]

I took a stack (approximately 5500 cards) and wrote a script which put 
the contents of one of the fields (an average of two to three syllables) 
into the name of each card. Saving the stack after this operation, I 
realized that its size had mushroomed from 1.3 MB to 7.1 MB. Suspecting 
corruption, I took another copy of the original stack and put instead the 
number of the card into its name. The result was pretty much the same. 

It might be a silly question, but why does it make such a huge difference 
in terms of stack size if every card is identified by a unique name?

Fritz